Diagnosis

Although the signs of inflammation in the blood are unspecific for rheumatic fever, they are typically present. The lowering of the blood cells (blood cell sedimentation rate, BSG) is accelerated and the C-reactive protein (CRP) is produced in increased quantities in the course of the inflammation. Further laboratory tests can determine whether a streptococcal infection has occurred: A throat swab can be taken to determine whether streptococci have colonized the upper airways.

For this test, a streptococcal antigen rapid test and the possibility of a culture of the smear are available. The concentration of antibodies directed against the bacteria (antistreptolysin and anti-DNAse-B) can be determined in a blood sample. The concentration of the antibody against streptolysin (antibody titer) only indicates acute inflammation if the value exceeds 300 IU (IU = international units).

The titer increases preferably in streptococcal infections of the nasopharynx, which is why it is of particular importance in the diagnosis of rheumatic fever. For the diagnosis of rheumatic fever, the Jones criteria, which were formulated in 1992 by the American Heart Association, are used. The presence of the disease is probable if it is possible to detect a previous streptococcal infection or if two main criteria or 1 main and 1 secondary criterion of the Jones criteria are met.

The primary criteria The secondary criteria include

Wandering polyarthritis (inflammation of joints, several joints are affected)
Carditis (inflammation of the heart)
Rheumatic nodules
Erythema anulare (circumscribed reddened areas of skin, especially on the trunk)
Chorea minor (involvement of the central nervous system with motor symptoms)
Fever
Joint pain (arthralgia)
Blood sedimentation rate accelerated and/or C-reactive protein increased
Change in the transmission of excitation to the heart

In addition to the clinical symptoms, the laboratory examination is an important criterion for the diagnosis of rheumatic fever. In the presence of rheumatic fever, the inflammatory parameters in the blood are elevated. These are the blood sedimentation rate (BSG) and the CRP value. For further diagnostics, antibodies against metabolic products of the bacteria causing the fever (streptococci) can be detected in the blood. An elevated titer of antibodies against “Streptolysin O” is a sign of a past infection in the throat, an elevated titer of antibodies against the enzyme “DNase B” indicates an infection in the skin area.