Rheumatic fever laboratory tests

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Varun Kumar, M.B.B.S.

Inflammatory Markers

The following inflammatory markers are often elevated:

• CBC: Leukocytosis
• C-reactive protein
• Erythrocyte sedimentation rate (ESR)

CRP and ESR help in monitoring the course of rheumatic fever during treatment as their levels normalizes with resolution of the condition.

Analysis of synovial fluid from arthritic joints in rheumatic fever may reveal leukocytosis with no crystals or organisms.

Diagnosis of Streptococcus Pharyngitis

• Throat culture for group A beta hemolytic streptococci may be performed. However many patients may have negative culture by the time rheumatic fever develops.
• Rapid streptococcal antigen test is quicker. However, it has a lower sensitivity (70%) and statistically equal specificity (98%) as throat culture. Therefore, negative test results rules out streptococcal infection.
• Elevated or rising antistreptolysin O antibody titer is often noted. The antibodies usually peak approximately during fourth or fifth week after the onset of infection. Patients should be tested at intervals of two weeks to detect raising titers. Antistreptococcal antibodies may also be noted in patients who are steptococcal carriers with asymptomatic pharyngitis.