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Viral Pharyngitis Workup

  • Author: KoKo Aung, MD, MPH, FACP; Chief Editor: Michael Stuart Bronze, MD  more...
Updated: Oct 22, 2015

Laboratory Studies

The similarity of signs and symptoms of viral pharyngitis make a specific etiological diagnosis virtually impossible without various laboratory tests. In many circumstances, etiological diagnosis is of no practical use because it may not alter the treatment and prognosis. Viral cultures are not needed to diagnose pharyngitis other than in a research setting.

The total WBC count may initially be slightly elevated without bandemia, followed by a decrease to fewer than 5000 cells/µL after 4-7 days of illness in about 50% of cases.

Atypical lymphocytosis is frequently associated with EBV and CMV infections.

Results from a rapid streptococcal antigen test and a bacterial culture of throat swab in viral pharyngitis may be positive (approximately 30% of patients with EBV infectious mononucleosis are colonized with group A streptococci).

Common cold

Specific virological diagnosis is unnecessary for practical purposes because it may not alter the management. Cultures of nasal secretions, serological tests, and polymerase chain reaction (PCR) techniques can be used for specific virological diagnosis. Rapid viral antigen detection tests are not sensitive enough to be useful.

EBV infectious mononucleosis

After week one of illness, peripheral blood film reveals relative and absolute lymphocytosis, with more than 10% atypical lymphocytes. Hemolytic anemia and thrombocytopenia secondary to anti-i antibodies are occasionally observed. Erythrocyte sedimentation rate (ESR) is elevated and liver function test results are mildly abnormal in about 90% of cases. Heterophile agglutination test (immunoglobulin M [IgM] antibody) results are positive with a titer of 40-fold or greater in 90% of affected adolescents and adults within the first few weeks after the onset of infectious mononucleosis symptoms. A mononucleosis spot test (Monospot) allows rapid screening for heterophile antibodies. Heterophile test results are usually negative in children younger than 4 years. Positive results for IgM antibody to viral capsid antigen and positive results for antibody to early antigen are useful to diagnose acute infection, particularly in cases that are heterophile negative.


Leukopenia and proteinuria are nonspecific findings in influenza. Virus isolation or detection of viral antigen in respiratory secretions is very useful to diagnose acute illness. Virus can be readily isolated from nasal swab specimens, throat swab specimens, nasal washes, or combined nose-and-throat swab specimens by inoculation of embryonated eggs or cell cultures. Rapid detection of viral antigen directly in respiratory secretions can be accomplished by immunofluorescent (IF) studies, time-resolved immunofluorescence assay (TRFIA), radioenzyme immunoassay, and enzyme-linked immunosorbent assay (ELISA).

PCR techniques have been described for rapid detection of influenza virus RNA in clinical samples. Serological tests can be used, but they are not helpful for diagnosis and treatment of acute disease secondary to delay in obtaining the antibody titers in convalescent sera. Serological tests are useful for epidemiological purposes. A rise in complement-fixing and hemagglutination-inhibiting antibody levels during the second week is considered diagnostic of acute infection.

Enterovirus infection

Positive results on an enteroviral-specific reverse transcriptase-polymerase chain reaction (RT-PCR) test of throat swabs are diagnostic. Etiological diagnosis is not necessary for clinical purposes because it may not alter treatment.

RSV infection

RSV antigen in nasal secretions can be reliably detected with commercially available rapid tests.

CMV infection

A relative lymphocytosis is characteristic of acute CMV pharyngitis. Atypical lymphocytes may represent 10% or more of the total. CMV can be readily isolated from a throat swab. Positive results on the CMV-specific IgM antibody titers are diagnostic of acute infection. Results of heterophile tests are usually negative (heterophile-negative mononucleosis syndrome). A 4-fold or greater rise in antibody titers is confirmatory but useful only for epidemiological purposes.

Acute retroviral syndrome (primary HIV infection)

Serological test results for HIV are usually negative during the phase of acute retroviral syndrome because the test takes approximately 4 weeks for seroconversion. HIV RNA assay by PCR technique and p24 antigen assay can be used to help confirm the diagnosis. HIV viral load is usually extremely high. The peripheral blood picture may resemble infectious mononucleosis. Heterophile test results are usually negative (heterophile-negative mononucleosis syndrome).

Contributor Information and Disclosures

KoKo Aung, MD, MPH, FACP Chief, Division of General Internal Medicine, O Roger Hollan Professor of Internal Medicine, Director, Office of Educational Programs, Department of Medicine, University of Texas Health Science Center at San Antonio

KoKo Aung, MD, MPH, FACP is a member of the following medical societies: American College of Physicians, Society of General Internal Medicine

Disclosure: Nothing to disclose.


Ambrish Ojha, MBBS 

Ambrish Ojha, MBBS is a member of the following medical societies: American College of Physicians, American Medical Association

Disclosure: Nothing to disclose.

Carson Lo, MD Consultant, West Houston Infectious Disease Associates

Carson Lo, MD is a member of the following medical societies: American College of Physicians-American Society of Internal Medicine, American Medical Association, American Society for Microbiology, American Society of Tropical Medicine and Hygiene, Infectious Diseases Society of America, Texas Medical Association

Disclosure: Nothing to disclose.

Specialty Editor Board

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

Disclosure: Received salary from Medscape for employment. for: Medscape.

Gordon L Woods, MD Consulting Staff, Department of Internal Medicine, University Medical Center

Gordon L Woods, MD is a member of the following medical societies: Society of General Internal Medicine

Disclosure: Nothing to disclose.

Chief Editor

Michael Stuart Bronze, MD David Ross Boyd Professor and Chairman, Department of Medicine, Stewart G Wolf Endowed Chair in Internal Medicine, Department of Medicine, University of Oklahoma Health Science Center; Master of the American College of Physicians; Fellow, Infectious Diseases Society of America

Michael Stuart Bronze, MD is a member of the following medical societies: Alpha Omega Alpha, American Medical Association, Oklahoma State Medical Association, Southern Society for Clinical Investigation, Association of Professors of Medicine, American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Additional Contributors

Gregory William Rutecki, MD Professor of Medicine, Fellow of The Center for Bioethics and Human Dignity, University of South Alabama College of Medicine

Gregory William Rutecki, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians, American Society of Nephrology, National Kidney Foundation, Society of General Internal Medicine

Disclosure: Nothing to disclose.

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