Rheumatic fever laboratory tests


 * Associate Editor(s)-In-Chief: Varun Kumar, M.B.B.S.

Overview
Patients with rheumatic fever often have elevated inflammatory markers such as ESR and C-reactive protein which help in monitoring the course of the disease. Presence of streptococcal infection can be established by obtaining throat culture or rapid streptococcal antigen test. Elevated or rising antistreptolysin O antibody titer is often noted. Endomyocardial biopsy demonstrate the presence of Aschoff bodies. However, biopsy is not recommended routinely.

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.

Biopsy of Endocardium
Though endomyocardial biopsy help in confirming the presence of carditis, it is not recommended as a routine diagnostic and prognostic tool as biopsy does not provide additional diagnostic information where clinical consensus is certain about diagnosis of carditis. Histopathologic findings include Aschoff bodies which are perivascular foci of esosinophilic collagen surrounded by lymphocytes, macrophages and plasma cells. These Aschoff bodies are eventually replaced by scar tissue.

Aschoff bodies (ie, perivascular foci of eosinophilic collagen surrounded by lymphocytes, plasma cells, and macrophages) are found in the pericardium, perivascular regions of the myocardium, and endocardium. The Aschoff bodies assume a granulomatous appearance with a central fibrinoid focus and eventually are replaced by nodules of scar tissue. Anitschkow cells are plump macrophages within Aschoff bodies. Anitschkow cells are cells associated with, and pathognomonic for, rheumatic heart disease. Anitschkow cells are enlarged macrophages found within granulomas (called Aschoff bodies) associated with the disease.