Asthma Workup

Author: Michael J Morris, MD; Chief Editor: Zab Mosenifar, MD more...

Updated: Apr 19, 2012

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Approach Considerations

Laboratory assessments and studies are not routinely indicated for the diagnosis of asthma, but they may be used to exclude other diagnoses. Eosinophilia and elevated serum IgE levels may help guide therapy in some cases. Arterial blood gases and pulse oximetry are valuable for assessing severity of exacerbations and following response to treatment.

Blood and Sputum Eosinophils

Blood eosinophilia greater than 4% or 300-400/μL supports the diagnosis of asthma, but an absence of this finding is not exclusionary. Eosinophil counts greater than 8% may be observed in patients with concomitant atopic dermatitis. This finding should prompt an evaluation for allergic bronchopulmonary aspergillosis, Churg-Strauss syndrome, or eosinophilic pneumonia.

In assessing asthma control, the British Thoracic Society recommends using sputum eosinophilia determinations to guide therapy. An improvement in asthma control, a decrease in hospitalizations, and a decrease in exacerbations were noted in those patients in whom sputum-guided therapy was used.^[56]A controlled prospective study has shown that adjusting inhaled corticosteroid (ICS) treatment to control sputum eosinophilia—as opposed to controlling symptoms, short-acting beta-agonist (SABA) use, nocturnal awakenings, and pulmonary function—significantly reduced both the rate of asthma exacerbations and the cumulative dose of inhaled corticosteroids.^[57]

Serum Immunoglobulin E

Total serum immunoglobulin E levels greater than 100 IU are frequently observed in patients experiencing allergic reactions, but this finding is not specific for asthma and may be observed in patients with other conditions (eg, allergic bronchopulmonary aspergillosis, Churg-Strauss syndrome). A normal total serum immunoglobulin E level does not exclude the diagnosis of asthma. Elevated serum IgE levels are required for chronic asthma patients to be treated with omalizumab (Xolair).

Arterial Blood Gas

Arterial blood gas (ABG) measurement provides important information in acute asthma. This test may reveal dangerous levels of hypoxemia or hypercarbia secondary to hypoventilation; typically, results are consistent with respiratory alkalosis. Because of the accuracy and utility of pulse oximetry, only patients whose oxygenation is not restored to over 90% with oxygen therapy require an ABG. The clinical picture usually obviates ABGs for most ED patients with acute asthma.

Venous levels of PCO₂ have been tested as a substitute for arterial measurements, and a venous PCO₂ greater than 45 mm may serve as a screening test but cannot substitute for the ABG evaluation of respiratory function.

Hypercarbia is of concern in that it reflects inadequate ventilation and may indicate the need for mechanical ventilation if the PCO₂ is elevated as a result of patient exhaustion; however, the decision to proceed with endotracheal intubation and mechanical ventilation is a clinical assessment.

Pulse Oximetry Assessment

Pulse oximetry measurement is desirable in all patients with acute asthma to exclude hypoxemia. The hypoxemia of uncomplicated acute asthma is readily reversible by oxygen administration. Oxygenation decreases 4-10 mm Hg with beta-agonist inhalant therapy due to increases in V/Q mismatch. Therefore, all patients with acute asthma should have oxygen saturation measured by pulse oximetry, or they simply should be placed on oxygen therapy.

In children, pulse oximetry is often used to grade severity of acute asthma. Oxygen saturation of 97% or above constitutes mild asthma, 92-97% constitutes moderate asthma, and less than 92% signifies severe asthma. Although an isolated pulse oximetry reading at triage is not predictive in most cases (with the notable exception of severe attacks that usually are self-evident on visual inspection), serial monitoring of pulse oximetry status can provide more subtle evidence for or against the need for hospital admission.

Chest Radiography

The chest radiograph remains the initial imaging evaluation in most individuals with symptoms of asthma. The value of chest radiography is in revealing complications or alternative causes of wheezing and the minor importance of wheezing in the diagnosis of asthma and its exacerbations. Chest radiography usually is more useful in the initial diagnosis of bronchial asthma than in the detection of exacerbations, although it is valuable in excluding complications such as pneumonia and asthma mimics, even during exacerbations.

In most patients with asthma, chest radiography findings are normal or may indicate hyperinflation. Findings may help rule out other pulmonary diseases such as allergic bronchopulmonary aspergillosis or sarcoidosis, which can manifest with symptoms of reactive airway disease. Chest radiography should be considered in all patients being evaluated for asthma to exclude other diagnoses.

Because pneumonia is one of the most common complications of asthma, chest radiography is indicated in patients with fever to rule out pneumonia. With new-onset asthma and eosinophilia, a radiograph may be useful in identifying prominent streaky infiltrates persisting less than 1 month, indicating Loeffler pneumonia. The infiltrates of Loeffler pneumonia are peripheral with central sparing of the lung fields. These findings have been described as the radiographic negative of pulmonary edema.

Patients with pleuritic chest pain or those with an acute asthmatic episode that responds poorly to therapy, require a chest film to exclude pneumothorax or pneumomediastinum, particularly if subcutaneous emphysema is present.

Chest CT Scanning

High-resolution CT (HRCT) is a second-line examination. It is useful in patients with chronic or recurring symptoms and in those with possible complications such as allergic bronchopulmonary aspergillosis and bronchiectasis.^[58]In the last decade, the role of CT in the imaging of airway disease increased after the development of lung HRCT. The technical progress of thin-section acquisition, high-spatial-frequency data reconstruction (ie, bone algorithm technique), and targeted reconstruction has allowed the visualization of finer details on HRCT scans; these details include airtrapping, measurable bronchial wall thickening, atelectasis, centrilobular nodules due to mucous plugging, and acinar nodules due to low-grade inflammatory changes.^[59]

HRCT findings in bronchial asthma include the following:

Bronchial wall thickening
Bronchial dilatation
Cylindrical and varicose bronchiectasis
Reduced airway luminal area
Mucoid impaction of the bronchi
Centrilobular opacities, or bronchiolar impaction
Linear opacities
Airtrapping, as demonstrated or exacerbated with expiration
Mosaic lung attenuation, or focal and regional areas of decreased perfusions

Note the images below.

High-resolution CT scan of the thorax obtained during inspiration demonstrates airtrapping in a patient with asthma. Inspiratory findings are normal.

High-resolution CT scan of the thorax obtained during expiration demonstrates a mosaic pattern of lung attenuation in a patient with asthma. Lucent areas (arrows) represent areas of airtrapping.

Electrocardiography

Patients with asthma who are severely symptomatic should undergo ECG monitoring, as with any seriously ill patient. Sinus tachycardia and ECG evidence of right heart strain are common in patients with acute asthma. The use of beta₂ -agonist therapy will cause a paradoxical decrease in heart rate as pulmonary function improves and symptoms are relieved. Supraventricular tachycardia raises the consideration of theophylline toxicity. Arrhythmias, other than supraventricular tachycardia, are rare.

MRI

Aside from cardiovascular applications, MRI of the thorax is used primarily as a problem-solving modality in the workup of patients with lung, mediastinal, or pleural lesions. MRI is a useful alternative to CT pulmonary angiography in evaluating possible pulmonary embolic disease in patients in whom iodinated contrast agent cannot be administered and when the avoidance of ionizing radiation is preferred. In bronchial asthma, the most promising work appears to involve the use of special paramagnetic gases, which amplify the low signal-to-noise ratio of conventional spin-echo and gradient-echo techniques by several thousand times. The use of such gases offsets the disadvantages of the large magnetic susceptibility states with consequent shortened T2 signals induced by the air-alveolar interfaces.

Nuclear Imaging

Nuclear medicine technology has been used in the study of aerosol and particulate distribution in the airways. Technetium-99m DTPA radioaerosol lung scintigraphy is a classic technique that shows the extent of major airway distribution, peripheral distribution (depending on particle size), and absorption in the oronasal air passages. Technetium-99m radioaerosol has been used to show improved peripheral lung distribution of corticosteroid both in normal persons and in persons treating their asthma using dry-powder inhalers as opposed to pressurized metered-dose inhalers (pMDIs) with a spacer device. Ventilation scanning with Technetium-99m DTPA has also been used as an indicator of ventilation defects in asthmatic children.

Allergy Skin Testing

Allergy skin testing is a useful adjunct in individuals with atopy. Results help guide indoor allergen mitigation or help diagnose allergic rhinitis symptoms. The allergens that most commonly cause asthma are aeroallergens such as house dust mites, animal danders, pollens, and mold spores. Two methods are available to test for allergic sensitivity to specific allergens in the environment: allergy skin tests and blood radioallergosorbent tests (RASTs). Allergy immunotherapy may be beneficial in controlling allergic rhinitis and asthma symptoms for some patients.

Pulmonary Function Testing

Spirometry assessments should be obtained as the primary test to establish the asthma diagnosis. Spirometry should be performed prior to initiating treatment in order to establish the presence and determine the severity of baseline airway obstruction.^[60]Optimally, the initial spirometry should also include measurements before and after inhalation of a short-acting bronchodilator in all patients in whom the diagnosis of asthma is considered. Spirometry measures the forced vital capacity (FVC), the maximal amount of air expired from the point of maximal inhalation, and the forced expiratory volume in one second (FEV₁). A reduced ratio of FEV₁ to FVC, when compared with predicted values, demonstrates the presence of airway obstruction. Reversibility is demonstrated by an increase of 12% and 200 mL after the administration of a short-acting bronchodilator.

As a preliminary assessment for exercise-induced asthma (EIA), or exercise-induced bronchospasm (EIB), perform spirometry in all patients with exercise symptoms to determine if any baseline abnormalities (ie, the presence of obstructive or restrictive indices) are present. The assessment and diagnosis of asthma cannot be based on spirometry findings alone because many other diseases are associated with obstructive spirometry indices.

Single-breath counting (SBC) is a novel technique for measuring pulmonary function in children. SBC is the measurement of how far an individual can count using a normal speaking voice after one maximal effort inhalation. The count is in cadence to a metronome that is set at 2 beats per second. A study by Ali et al determined that SBC correlates well with standard measures of pulmonary function.^[61]However, further studies are needed to establish values and to evaluate the use in an ED population of patients with acute asthma exacerbation.

Methacholine/histamine challenge

Bronchoprovocation testing with either methacholine or histamine is useful when spirometry findings are normal or near normal, especially in patients with intermittent or exercise-induced asthma symptoms. Bronchoprovocation testing helps determine if airway hyperreactivity is present, and a negative test result usually excludes the diagnosis of asthma.

Trained individuals should perform this asthma testing in an appropriate facility and in accordance with the guidelines of the American Thoracic Society published in 1999.^[62]Methacholine is administered in incremental doses up to a maximum dose of 16 mg/mL, and a 20% decrease in FEV₁, up to the 4 mg/mL level, is considered a positive test result for the presence of bronchial hyperresponsiveness. The presence of airflow obstruction with an FEV₁ less than 65-70% at baseline is generally an indication to avoid performing the test.

Eucapnic hyperventilation

Eucapnic hyperventilation with either cold or dry air is an alternative method of bronchoprovocation testing. It has been used to evaluate patients for exercise-induced asthma and has been shown to produce results similar to those of methacholine-challenge asthma testing.

Exercise testing

Exercise spirometry is the standard method for assessing patients with exercise-induced bronchospasm. Testing involves 6-10 minutes of strenuous exertion at 85-90% of predicted maximal heart rate and measurement of postexercise spirometry for 15-30 minutes. The defined cutoff for a positive test result is a 15% decrease in FEV₁ after exercise.

Exercise testing may be accomplished in 3 different ways, using cycle ergometry, a standard treadmill test, or free running exercise. This method of testing is limited because laboratory conditions may not subject the patient to the usual conditions that trigger exercise-induced bronchospasm symptoms, and results have a lower sensitivity for asthma than other methods.

Allergen-inhalation challenge

Allergen-inhalation challenges can be performed in selected patients but are generally not needed or recommended. This test requires an available allergen solution and specialized centers able to handle potentially significant reactions. A negative test finding may allow continued exposure to an allergen (eg, family pet); a positive test finding can dramatically indicate that the patient should avoid a particular allergen. This test is often needed to help diagnose occupational asthma.

Peak Flow Monitoring

Peak expiratory flow (PEF) measurement is common in the ED because it is inexpensive and portable. Serial measurements document response to therapy and, along with other parameters, are helpful in determining whether to admit the patient to the hospital or discharge from the ED. A limitation of PEF is that it is dependent on effort by the patient. FEV₁ is also effort dependent but less so than PEF. FEV₁ is not often used in the ED except in research settings.

PEF in the ED can be compared with asymptomatic (baseline) PEF, if known. Unfortunately, patients often do not know their asymptomatic PEF. Moreover, the reference group for the ideal PEF percent predicted (based on age, sex, height) may not be accurate for the patient population seen in many inner-city EDs, since most equations are based on white populations.

Exhaled Nitric Oxide

Exhaled nitric oxide analysis has been shown to predict airway inflammation and asthma control; however, it is technically more complex and not routinely used in the monitoring of patients with asthma.

A prospective, controlled study has shown that when inhaled corticosteroid asthma treatment was adjusted to control the fraction of exhaled nitric oxide, as opposed to controlling the standard indices of asthma, the cumulative dose of ICS was reduced, with no worsening of the frequency of asthma exacerbations.^[63]

Sinus CT Scanning

Sinus CT scanning may be useful to help exclude acute or chronic sinusitis as a contributing factor. In patients with chronic sinus symptoms, CT scanning of the sinuses can also help rule out chronic sinus disease. Conventional wisdom regarding the sinus radiographic evaluation of chronic coughing and asthma suggests that a workup for chronic coughing should be performed first, as outlined in a Finnish study of hospital admissions for acute asthma. Admission chest radiographs showed abnormalities in 50% of the patients and resulted in treatment changes in 5%. The numbers were more remarkable when a paranasal sinus series was obtained in unselected patients who presented primarily because of asthma.

A sinus abnormality of any kind was found in 85% of patients; maxillary sinus abnormalities occurred alone in 63%. In 29% of patients with a sinus abnormality, treatment was immediately altered. All abnormalities were identified on the Waters view alone, which is 6 times more useful than chest radiography in directing the treatment of acute asthma.^{[64, 65]}

24-Hour pH Monitoring

A 24-hour pH probe (the Bravo study is now possible in selected centers) can be used to help diagnose gastroesophageal reflux disease (GERD) if a patient’s condition is refractory to asthma therapy. Empirical medical therapy is often tried without performing diagnostic tests for GERD, especially if a patient has symptoms of GERD. In cases of GERD, a prolonged trial of therapy may be necessary. The median time to improvement of GERD-induced cough has been reported as 3 months.^[66]

Histologic Findings

Asthma is an inflammatory disease characterized by the recruitment of inflammatory cells, vascular congestion, increased vascular permeability, increased tissue volume, and the presence of an exudate. Eosinophilic infiltration, a universal finding, is considered a major marker of the inflammatory activity of the disease.

Histologic evaluations of the airways in a typical patient reveal infiltration with inflammatory cells, narrowing of airway lumina, bronchial and bronchiolar epithelial denudation, and mucus plugs. Additionally, a patient with severe asthma may have a markedly thickened basement membrane and airway remodeling in the form of subepithelial fibrosis and smooth muscle hypertrophy or hyperplasia.

Proceed to Treatment & Management

Contributor Information and Disclosures

Author

Michael J Morris, MD Clinical Assistant Professor, Pulmonary Disease/Critical Care Service, Department of Medicine, Brooke Army Medical Center; Associate Program Director, Internal Medicine Residency, San Antonio Uniformed Services Health Education Consortium

Michael J Morris, MD is a member of the following medical societies: American Association for Respiratory Care, American College of Chest Physicians, American College of Physicians, American Thoracic Society, and Association of Military Surgeons of the US

Disclosure: Pfizer/Boehringer-Ingelheim Honoraria Speaking and teaching

Coauthor(s)

Gregory J Argyros Col, MD Director, Education, Training, and Research, J7/Joint Task Force, National Capital Region Medical; Professor of Medicine, Uniformed Services University of the Health Sciences

Gregory J Argyros Col, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Chest Physicians, American College of Physicians-American Society of Internal Medicine, and American Thoracic Society

Disclosure: Nothing to disclose.

Stephen G Batuello, MD Consulting Staff, Colorado ENT Specialists

Stephen G Batuello, MD is a member of the following medical societies: American Academy of Otolaryngology-Head and Neck Surgery, American College of Physician Executives, American Medical Association, and Colorado Medical Society

Disclosure: Nothing to disclose.

Edward Bessman, MD, MBA Chairman and Clinical Director, Department of Emergency Medicine, John Hopkins Bayview Medical Center; Assistant Professor, Department of Emergency Medicine, Johns Hopkins University School of Medicine

Edward Bessman, MD, MBA is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Paul Blackburn, DO, FACOEP, FACEP Attending Physician, Department of Emergency Medicine, Maricopa Medical Center

Paul Blackburn, DO, FACOEP, FACEP is a member of the following medical societies: American College of Emergency Physicians, American College of Osteopathic Emergency Physicians, American Medical Association, and Arizona Medical Association

Disclosure: Nothing to disclose.

Barry E Brenner, MD, PhD, FACEP Professor of Emergency Medicine, Professor of Internal Medicine, Program Director for Emergency Medicine, Case Medical Center, University Hospitals, Case Western Reserve University School of Medicine

Barry E Brenner, MD, PhD, FACEP is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Chest Physicians, American College of Emergency Physicians, American College of Physicians, American Heart Association, American Thoracic Society, Arkansas Medical Society, New York Academy of Medicine, New York Academy of Sciences, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Praveen Buddiga, MD Physician, Allergy, Asthma and Immunology, Baz Allergy, Asthma and Sinus Center, Fresno, California

Praveen Buddiga, MD, is a member of the following medical societies: American Academy of Allergy Asthma and Immunology and American College of Allergy, Asthma and Immunology

Disclosure: Meda Honoraria Speaking and teaching; Teva Honoraria Speaking and teaching; AstraZeneca Honoraria Speaking and teaching

Robert K Bush, MD Professor of Medicine (CHS, Emeritus), University of Wisconsin School of Medicine and Public Health; Chief of Allergy (retired), William S Middleton Veterans Affairs Hospital

Robert K Bush, MD is a member of the following medical societies: American Academy of Allergy Asthma and Immunology and American College of Physicians

Disclosure: University of WI- Madison Emeritus- Reitred; Wm S. Middleton VA Hospital Retired Retired; Teva Pharmaceuticals IRA Holding None; Associate Editor Journal Allergy Clinical Immunology Honoraria None

Michael R Bye, MD Professor of Clinical Pediatrics, Division of Pulmonary Medicine, Columbia University College of Physicians and Surgeons; Attending Physician, Pediatric Pulmonary Medicine, Morgan Stanley Children's Hospital of New York Presbyterian, Columbia University Medical Center

Michael R Bye, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Chest Physicians, and American Thoracic Society

Disclosure: Nothing to disclose.

Charles Callahan, DO Professor, Deputy Chief of Clinical Services, Walter Reed Army Medical Center

Charles Callahan, DO is a member of the following medical societies: American Academy of Pediatrics, American College of Chest Physicians, American College of Osteopathic Pediatricians, American Thoracic Society, Association of Military Surgeons of the US, and Christian Medical & Dental Society

Disclosure: Nothing to disclose.

Peter G Canaday, MD Private Practice, Consultant Radiologist, Dakota Dunes, SD

Peter G Canaday, MD is a member of the following medical societies: American College of Chest Physicians, American College of Radiology, American Medical Association, American Roentgen Ray Society, Nebraska Medical Association, Radiological Society of North America, Society of Breast Imaging, and Society of Thoracic Radiology

Disclosure: Nothing to disclose.

G Patricia Cantwell, MD, FCCM Professor of Clinical Pediatrics, Chief, Division of Pediatric Critical Care Medicine, University of Miami, Leonard M Miller School of Medicine; Medical Director, Palliative Care Team, Director, Pediatric Critical Care Transport, Holtz Children's Hospital, Jackson Memorial Medical Center; Medical Manager, FEMA, Urban Search and Rescue, South Florida, Task Force 2; Pediatric Medical Director, Tilli Kids – Pediatric Initiative, Division of Hospice Care Southeast Florida, Inc

G Patricia Cantwell, MD, FCCM is a member of the following medical societies: American Academy of Hospice and Palliative Medicine, American Academy of Pediatrics, American Heart Association, American Trauma Society, National Association of EMS Physicians, Society of Critical Care Medicine, and Wilderness Medical Society

Disclosure: Nothing to disclose.

Lanny Garth Close, MD Chair, Professor, Department of Otolaryngology-Head and Neck Surgery, Columbia University College of Physicians and Surgeons

Lanny Garth Close, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Facial Plastic and Reconstructive Surgery, American Academy of Otolaryngology-Head and Neck Surgery, American College of Physicians, American Laryngological Association, American Society for Head and Neck Surgery, and New York Academy of Medicine

Disclosure: Nothing to disclose.

Cheryl D Courtlandt, MD Faculty, Department of Pediatrics, University of North Carolina at Chapel Hill School of Medicine; Medical Director, Pediatric Asthma Program, Attending Physician, Department of Pediatrics, Levine Children's Hospital, Carolinas Medical Center

Cheryl D Courtlandt, MD is a member of the following medical societies: Ambulatory Pediatric Association, American Academy of Pediatrics, and National Medical Association

Disclosure: Nothing to disclose.

Stephen C Dreskin, MD, PhD Professor of Medicine, Departments of Internal Medicine, Director of Allergy, Asthma, and Immunology Practice, University of Colorado Health Sciences Center

Stephen C Dreskin, MD, PhD is a member of the following medical societies: American Academy of Allergy Asthma and Immunology, American Association for the Advancement of Science, American Association of Immunologists, American College of Allergy, Asthma and Immunology, Clinical Immunology Society, and Joint Council of Allergy, Asthma and Immunology

Disclosure: Genentech, Inc. Consulting fee Consulting; Clinical Immunization and Safety Assessment (CISA) Network (CDC) administered by America's Health Insurance Plans (AHIP) Consulting fee Consulting; Genentech, Inc. Grant/research funds Other; Medical Expert Panel, Department of Health and Human Services, Division of Vaccine Injury Compensation None Independent contractor; American Board of Allergy and Immunology Honoraria Board membership; Novartis, Inc Consulting fee Review panel membership

Pamela L Dyne, MD Professor of Clinical Medicine/Emergency Medicine, University of California, Los Angeles, David Geffen School of Medicine; Attending Physician, Department of Emergency Medicine, Olive View-UCLA Medical Center

Pamela L Dyne, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Barry J Evans, MD Assistant Professor of Pediatrics, Temple University Medical School; Director of Pediatric Critical Care and Pulmonology, Associate Chair for Pediatric Education, Temple University Children's Medical Center

Barry J Evans, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Chest Physicians, American Thoracic Society, and Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Michael R Filbin, MD Clinical Instructor, Department of Emergency Medicine, Massachusetts General Hospital

Michael R Filbin, MD is a member of the following medical societies: American College of Emergency Physicians, Massachusetts Medical Society, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Joseph P Garry, MD, FACSM, FAAFP Associate Professor, Department of Family and Community Medicine, University of Minnesota Medical School

Joseph P Garry, MD, FACSM, FAAFP is a member of the following medical societies: American Academy of Family Physicians, American College of Sports Medicine, American Heart Association, American Medical Society for Sports Medicine, and Minnesota Medical Association

Disclosure: Nothing to disclose.

Murray Grossan, MD Consulting Staff, Tower Ear, Nose and Throat

Murray Grossan, MD is a member of the following medical societies: American Medical Association, American Tinnitus Association, California Medical Association, and Los Angeles County Medical Association

Disclosure: Hydro Med Inc Ownership interest Management position

Payel Gupta, MD Department of Allergy and Immunology, ENT Faculty Practice

Payel Gupta, MD is a member of the following medical societies: American College of Physicians

Disclosure: Nothing to disclose.

William F Kelly III, MD Assistant Professor of Medicine, Uniformed Services University of the Health Sciences; Staff Physician, Division of Pulmonary/Critical Care Medicine, Department of Medicine, Walter Reed Army Medical Center

William F Kelly III, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Chest Physicians, and American College of Physicians

Disclosure: Nothing to disclose.

Rick Kulkarni, MD Attending Physician, Department of Emergency Medicine, Cambridge Health Alliance, Division of Emergency Medicine, Harvard Medical School

Rick Kulkarni, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Emergency Physicians, American Medical Association, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine

Disclosure: WebMD Salary Employment

Eugene C Lin, MD Attending Radiologist, Teaching Coordinator for Cardiac Imaging, Radiology Residency Program, Virginia Mason Medical Center; Clinical Assistant Professor of Radiology, University of Washington School of Medicine

Eugene C Lin, MD is a member of the following medical societies: American College of Nuclear Medicine, American College of Radiology, Radiological Society of North America, and Society of Nuclear Medicine

Disclosure: Nothing to disclose.

Markus Little, MD Resident Physician, Department of Emergency Medicine, State University of New York Downstate Medical Center

Disclosure: Nothing to disclose.

Jeffrey A Miller, MD Associate Adjunct Professor of Clinical Radiology, University of Medicine and Dentistry of New Jersey-New Jersey Medical School; Faculty, Department of Radiology, Veterans Affairs of New Jersey Health Care System

Jeffrey A Miller, MD is a member of the following medical societies: American Roentgen Ray Society, Society for Health Services Research in Radiology, and Society of Thoracic Radiology

Disclosure: Nothing to disclose.

Daniel R Neuspiel, MD, MPH, FAAP Director of Ambulatory Pediatrics, Levine Children's Hospital, Carolinas Medical Center; Adjunct Clinical Professor of Pediatrics, University of North Carolina School of Medicine

Daniel R Neuspiel, MD, MPH, FAAP is a member of the following medical societies: American Academy of Pediatrics, American College of Physician Executives, American Public Health Association, New York Academy of Medicine, and Phi Beta Kappa

Disclosure: Nothing to disclose.

John D Newell Jr, MD Professor of Radiology, Head, Division of Radiology, National Jewish Health; Professor, Department of Radiology, University of Colorado School of Medicine

John D Newell Jr, MD is a member of the following medical societies: American College of Chest Physicians, American College of Radiology, American Roentgen Ray Society, American Thoracic Society, Association of University Radiologists, Radiological Society of North America, and Society of Thoracic Radiology

Disclosure: Siemens Medical Grant/research funds Consulting; Vida Corporation Ownership interest Board membership; TeraRecon Grant/research funds Consulting; eMedicine Honoraria Consulting; Humana Press Honoraria Other

John J Oppenheimer, MD Clinical Associate Professor, Department of Medicine, University of Medicine and Dentistry of New Jersey; Director of Clinical Research, Pulmonary and Allergy Associates, PA

John J Oppenheimer, MD is a member of the following medical societies: American Academy of Allergy Asthma and Immunology and American College of Allergy, Asthma and Immunology

Disclosure: AZ Consulting fee Consulting; AZ Grant/research funds Independent contractor; Glaxo Consulting fee Consulting; Glaxo Grant/research funds Independent contractor; Merck Consulting fee Consulting; Merck Grant/research funds Independent contractor; SRXA Consulting

Stephen Rosenfeld, MD Professor Emeritus, Department of Medicine, Allergy, Immunology and Rheumatology Unit, University of Rochester School of Medicine and Dentistry

Stephen Rosenfeld, MD is a member of the following medical societies: American Academy of Allergy Asthma and Immunology, American Association of Immunologists, American Federation for Clinical Research, Clinical Immunology Society, and Medical Society of the State of New York

Disclosure: Nothing to disclose.

Constantine K Saadeh, MD President, Allergy ARTS, LLP; Principal Investigator, Amarillo Center for Clinical Research, Ltd

Constantine K Saadeh, MD is a member of the following medical societies: American Academy of Allergy Asthma and Immunology, American College of Rheumatology, American Medical Association, Southern Medical Association, and Texas Medical Association

Disclosure: Nothing to disclose.

Anthony J Saglimbeni, MD President, South Bay Sports and Preventive Medicine Associates; Private Practice; Team Internist, San Francisco Giants; Team Internist, West Valley College; Team Physician, Bellarmine College Prep; Team Physician, Presentation High School; Team Physician, Santa Clara University; Consultant, University of San Francisco, Academy of Art University, Skyline College, Foothill College, De Anza College

Anthony J Saglimbeni, MD, is a member of the following medical societies: California Medical Association and Santa Clara County Medical Association

Disclosure: South Bay Sports and Preventive Medicine Associates, Inc Ownership interest Other

Assaad J Sayah, MD Chief, Department of Emergency Medicine, Cambridge Health Alliance

Assaad J Sayah, MD is a member of the following medical societies: National Association of EMS Physicians

Disclosure: Nothing to disclose.

Thomas Scanlin, MD Chief, Division of Pulmonary Medicine and Cystic Fibrosis Center, Department of Pediatrics, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School

Thomas Scanlin, MD is a member of the following medical societies: American Association for the Advancement of Science, American Society for Biochemistry and Molecular Biology, American Thoracic Society, Society for Pediatric Research, and Society for Pediatric Research

Disclosure: Nothing to disclose.

Adam J Schwarz, MD Consulting Staff, Critical Care Division, Pediatric Subspecialty Faculty, Children's Hospital of Orange County

Adam J Schwarz, MD is a member of the following medical societies: American Academy of Pediatrics and Phi Beta Kappa

Disclosure: Nothing to disclose.

Girish D Sharma, MD Professor of Pediatrics, Rush Medical College; Senior Attending, Department of Pediatrics, Director, Section of Pediatric Pulmonology and Rush Cystic Fibrosis Center, Rush University Medical Center

Girish D Sharma, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Chest Physicians, American Thoracic Society, and Royal College of Physicians of Ireland

Disclosure: Nothing to disclose.

Richard H Sinert, DO Professor of Emergency Medicine, Clinical Assistant Professor of Medicine, Research Director, State University of New York College of Medicine; Consulting Staff, Department of Emergency Medicine, Kings County Hospital Center

Richard H Sinert, DO is a member of the following medical societies: American College of Physicians and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

William W Storms, MD Clinical Professor, University of Colorado Health Sciences Center; Private Practice, The William Storms Allergy Clinic, Colorado Springs, Colorado

Disclosure: AstraZeneca Honoraria Speaking and teaching; Merck Grant/research funds None; Merck Honoraria Consulting; Merck Honoraria Speaking and teaching; Strategic Pharmaceutical Advisors Honoraria Consulting; TEVA Honoraria Consulting; TEVA Speaking and teaching; TREAT Foundation Honoraria Consulting; TEVA Grant/research funds Other; Alcon Labs Grant/research funds Other

Russell D White, MD Professor of Medicine, Professor of Orthopedic Surgery, Director of Sports Medicine Fellowship Program, Medical Director, Sports Medicine Center, Head Team Physician, University of Missouri-Kansas City Intercollegiate Athletic Program, Department of Community and Family Medicine, University of Missouri-Kansas City School of Medicine, Truman Medical Center-Lakewood

Russell D White, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Family Physicians, American Association of Clinical Endocrinologists, American College of Sports Medicine, American Diabetes Association, and American Medical Society for Sports Medicine

Disclosure: Nothing to disclose.

Craig C Young, MD Professor, Departments of Orthopedic Surgery and Community and Family Medicine, Medical Director of Sports Medicine, Director of Primary Care Sports Medicine Fellowship, Medical College of Wisconsin

Craig C Young, MD is a member of the following medical societies: American Academy of Family Physicians, American College of Sports Medicine, American Medical Society for Sports Medicine, and Phi Beta Kappa

Disclosure: Nothing to disclose.

Mark Zwanger, MD, MBA Assistant Professor, Department of Emergency Medicine, Jefferson Medical College of Thomas Jefferson University

Mark Zwanger, MD, MBA is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, and American Medical Association

Disclosure: Nothing to disclose.

Specialty Editor Board

Michael A Kaliner, MD Clinical Professor of Medicine, George Washington University School of Medicine; Chief, Section of Allergy and Immunology, Washington Hospital Center; Medical Director, Institute for Asthma and Allergy

Michael A Kaliner, MD is a member of the following medical societies: American Academy of Allergy Asthma and Immunology, American Association of Immunologists, American College of Allergy, Asthma and Immunology, American Society for Clinical Investigation, American Thoracic Society, and Association of American Physicians

Disclosure: Alcon Consulting fee Consulting; Teva Consulting fee Consulting; Meda Honoraria Speaking and teaching; Ista Consulting fee Consulting; sunovian Consulting fee Consulting; dey Honoraria Review panel membership

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

Robert E O'Connor, MD, MPH Professor and Chair, Department of Emergency Medicine, University of Virginia Health System

Robert E O'Connor, MD, MPH is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American College of Physician Executives, American Heart Association, American Medical Association, Medical Society of Delaware, National Association of EMS Physicians, Society for Academic Emergency Medicine, and Wilderness Medical Society

Disclosure: Nothing to disclose.

Arlen D Meyers, MD, MBA Professor of Otolaryngology, Dentistry, and Engineering, University of Colorado School of Medicine

Arlen D Meyers, MD, MBA is a member of the following medical societies: American Academy of Facial Plastic and Reconstructive Surgery, American Academy of Otolaryngology-Head and Neck Surgery, and American Head and Neck Society

Disclosure: Covidien Corp Consulting fee Consulting; US Tobacco Corporation Unrestricted gift Unknown; Axis Three Corporation Ownership interest Consulting; Omni Biosciences Ownership interest Consulting; Sentegra Ownership interest Board membership; Medvoy Ownership interest Management position; Cerescan Imaging Consulting; Headwatersmb Consulting fee Consulting; Venturequest Royalty Consulting

Chief Editor

Zab Mosenifar, MD Director, Division of Pulmonary and Critical Care Medicine, Director, Women's Guild Pulmonary Disease Institute, Professor and Executive Vice Chair, Department of Medicine, Cedars Sinai Medical Center, University of California, Los Angeles, David Geffen School of Medicine

Zab Mosenifar, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, American Federation for Medical Research, and American Thoracic Society

Disclosure: Nothing to disclose.

Additional Contributors

The authors and editors of eMedicine gratefully acknowledge the contributions of previous authors Michael Goldman, MD, Jan Malacara, PA-C, Rohit K Katial, MD, A Antoine Kazzi, MD, Araz Marachelian, MD, and Jannette Collins, MD, MEd, FCCP, to the development and writing of the source articles.

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Asthma treatment. Asthma causes and symptoms. Antigen presentation by the dendritic cell with the lymphocyte and cytokine response leading to airway inflammation and asthma symptoms.

Asthma treatment. Asthma symptoms and severity. Recommended guidelines for determination of asthma severity based on clinical symptoms, exacerbations, and measurements of airway function. Adapted from Global Strategy for Asthma Management and Prevention: 2002 Workshop Report.

Asthma treatment. Stepwise approach to pharmacological management of asthma based on asthma severity. Adapted from Global Strategy for Asthma Management and Prevention: 2002 Workshop Report.

Asthma. High-resolution CT scan of the thorax obtained during inspiration in a patient with recurrent left lower lobe pneumonia shows a bronchial mucoepidermoid carcinoma (arrow).

Asthma. High-resolution CT scan of the thorax obtained during expiration in a patient with recurrent left lower lobe pneumonia shows a bronchial mucoepidermoid carcinoma. Note the normal increase in right lung attenuation during expiration (right arrow). The left lung remains lucent, especially the upper lobe, secondary to bronchial obstruction with airtrapping (left upper arrow). The vasculature on the left is diminutive, secondary to reflex vasoconstriction. Left pleural thickening and abnormal linear opacities are noted in the left lower lobe; these are the result of prior episodes of postobstructive pneumonia (left lower arrow).

High-resolution CT scan of the thorax obtained during inspiration demonstrates airtrapping in a patient with asthma. Inspiratory findings are normal.

High-resolution CT scan of the thorax obtained during expiration demonstrates a mosaic pattern of lung attenuation in a patient with asthma. Lucent areas (arrows) represent areas of airtrapping.

Posteroanterior chest radiograph demonstrates a pneumomediastinum in bronchial asthma. Mediastinal air is noted adjacent to the anteroposterior window and airtrapping extends to the neck, especially on the right side.

Lateral chest radiograph demonstrates a pneumomediastinum in bronchial asthma. Air is noted anterior to the trachea (same patient as in the previous image).

High-resolution CT scan of the thorax obtained during inspiration demonstrates airtrapping in a patient with asthma. Inspiratory findings are normal.

High-resolution CT scan of the thorax obtained during expiration demonstrates a mosaic pattern of lung attenuation in a patient with asthma. Lucent areas (arrows) represent areas of airtrapping (same patient as in the previous image).

Asthma. High-resolution CT scan of the thorax obtained during inspiration in a patient with recurrent left lower lobe pneumonia shows a bronchial mucoepidermoid carcinoma (arrow).

Asthma. High-resolution CT scan of the thorax obtained during expiration in a patient with recurrent left lower lobe pneumonia shows a bronchial mucoepidermoid carcinoma (same patient as in the previous image). Note the normal increase in right lung attenuation during expiration (right arrow). The left lung remains lucent, especially the upper lobe, secondary to bronchial obstruction with airtrapping (left upper arrow). The vasculature on the left is diminutive, secondary to reflex vasoconstriction. Left pleural thickening and abnormal linear opacities are noted in the left lower lobe; these are the result of prior episodes of postobstructive pneumonia (left lower arrow).

Asthma. High-resolution CT scan of the thorax demonstrates mild bronchial thickening and dilatation in a patient with bilateral lung transplants and bronchial asthma.

Asthma. High-resolution CT scan of the thorax demonstrates central bronchiectasis, a hallmark of allergic bronchopulmonary aspergillosis (right arrow), and the peripheral tree-in-bud appearance of centrilobular opacities (left arrow), which represent mucoid impaction of the small bronchioles.

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