Tuberculous pericarditis laboratory tests


 * Associate Editor-In-Chief: Varun Kumar, M.B.B.S.; Lakshmi Gopalakrishnan, M.B.B.S.

Tuberculin skin test
Patients with tuberculous pericarditis most often have a positive PPD test. However immunocompromised patients such as those with HIV infection may have false negative tuberculin test. In developing countries where TB is endemic, the tuberculin skin test may be of little value secondary to high prevalence of TB and BCG vaccination.

Pericardiocentesis
Pericardiocentesis should be performed in patients with cardiac tamponade, a large symptomaticpericardial effusion, an effusion that does not resolve with traditional treatment (NSAIDs), and an effusion that is suspected to be due to malignancy, a bacterial infection or tuberculosis. Among patients with tuberculous pericarditis, the pericardial fluid is blood-stained in approximately 80% of patients. Tuberculous pericardial fluid is often exudative with high protein, LDH and leukocyte levels. This fluid can be used to test for the presence of acid-fast bacilli which may be detected in up to approximately 40% of patients with tuberculous pericarditis. Culturing the sample may increase the bacterial yield. If pericardiocentesis is not diagnostic, a pericardial biopsy may be performed. However, less invasive studies such as sputum examination, gastric washings, urine culture, and right scalene lymph node biopsy may be tried before biopsy.


 * Polymerase chain reaction(PCR) is another test that helps in detecting presence of DNA of Mycobacterium tuberculosis  . However PCR is found to have low sensitivity and high false positive results in detection of mycobacterium in pericardial fluid.


 * Adenosine deaminase(ADA) is an enzyme produced by leukocytes. Measurement of ADA levels in pericardial fluid is found to be of diagnostic value in tuberculous pericardial disease . ADA levels of ≥40units/liter in pericardial fluid has a sensitivity of 87% and specificity of 89%.


 * Measurement of interferon-gamma in pericardial fluid is another diagnostic test with a high sensitivity and a specificity of 100%, using a cutoff level of >200pg/L (n=30) . Sensitivity and specificity and positive predective value were 92%, 100% and 100% respectively in another South African series in the region where the prevalence of TB is high. Further studies with a larger sample size may provide further evidence to support the routine use of this test in the diagnosis of TB pericarditis.

Pericardial biopsy
Pericardial biopsy may be associated with morbidity and prolongation of the hospital stay. Sensitivity of this test in diagnosing TB ranges between 10-64%. Therefore, a normal biopsy finding does not exclude TB. The probability of obtaining a definitive bacteriological result is greatest when pericardial fluid and biopsy specimens are examined early in the effusive stage.