Pseudomonas aeruginosa Infections Workup

Updated: Dec 05, 2016
  • Author: Marcus Friedrich, MD, MBA, FACP; Chief Editor: Michael Stuart Bronze, MD  more...
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Workup

Laboratory Studies

CBC count

A CBC count may reveal leukocytosis with a left shift and bandemia. In patients with hematologic malignancy or status postchemotherapy, leukopenia with neutropenia is expected. Leukopenia is a poor prognostic indicator.

Blood cultures

Obtain at least 2 sets of blood cultures (2 aerobic, 2 anaerobic bottles) from different sites.

Positive results on blood culture in the absence of extracardiac sites of infection may indicate pseudomonal endocarditis. However, bacteremia may complicate intravenous catheter infections, urinary tract instrumentation, trauma, and surgery in the absence of endocarditis.

Other cultures

In UTI, urinalysis is helpful in determining a diagnosis. Culture confirms the diagnosis and provides information concerning antibiotic susceptibility.

In pneumonia, sputum and respiratory secretions should be cultured. However, the isolation of Pseudomonas from sputum and tracheal secretions might indicate airway colonization. The poor sensitivity and specificity of sputum in determining the bacterial cause of pneumonia in patients who are mechanically ventilated has led to greater use of quantitative cultures obtained from protected bronchoalveolar lavage and protected specimen brushings. Blood gas analysis to evaluate for hypoxia or hypercarbia should also be performed in patients with pneumonia.

Obtain wound and burn cultures and cultures from other body fluids and secretions according to the clinical scenario. To aid in diagnosis, obtaining burn wound biopsies with quantitative bacterial cultures is recommended. A bacterial count of greater than 105 organisms per gram of tissue is diagnostic of a burn wound infection.

Gram stain

Obtain Gram stain and culture of cerebrospinal fluid if meningitis is suspected.

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Imaging Studies

Chest radiography

Abnormalities observed in pseudomonal pneumonia depend on the pathogenesis of the infections. In primary pseudomonal pneumonia, in which aspiration of infected secretions results in pneumonia, the chest radiograph often reveals bilateral bronchopneumonia consisting of nodular infiltrates with or without pleural effusion. Lobar pneumonia is uncommon.

Early pulmonary vascular congestion is found in patients with bacteremic pseudomonal pneumonia and rapidly progresses to pulmonary edema and necrotizing bronchopneumonia. Within 48-72 hours, the radiograph demonstrates a mixture of alveolar and interstitial infiltrates, and cavitation may be present.

Bone scan

Triple-phase bone scan may be useful in patients with suspected skeletal infection, although many would preferentially rely on MRI.

Brain CT scan or MRI

Brain CT scan or MRI allows for evaluation of patients suspected of having a pseudomonal brain abscess.

Renal ultrasonography

Renal ultrasonography is useful in evaluating patients suspected of having a perinephric abscess complicating UTI.

Echocardiography

Echocardiography should be considered in patients with positive blood culture findings in whom endocarditis is suspected. Normal transthoracic echocardiography findings do not rule out endocarditis in patients in whom clinical suspicion is high. Transesophageal echocardiography should then be considered.

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Other Tests

See the list below:

  • Gram stain of respiratory secretions and cerebrospinal fluid
  • Fluorescein staining and slit-lamp examination of the cornea for keratitis
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Procedures

Procedures indicated for pseudomonal infections depend on the clinical picture and the site of infection.

Flexible fiberoptic bronchoscopy with bronchoalveolar lavage or bronchial brushing may be useful in pneumonia. Pleural effusions may require thoracocentesis.

Lumbar puncture with cell count and cultures is indicated in suspected pseudomonal meningitis.

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Histologic Findings

Pseudomonas infection causes necrotizing inflammation. Histologically, gram-negative rods are observed in the walls of blood vessels, causing coagulation necrosis, along with thrombosis and hemorrhage.

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