Increased pleural adenosine deaminase is diagnostic for:
Tuberculous effusions can now be diagnosed accurately by increased levels of pleural fluid adenosine deaminase (above 40 U/L) (REF. SCHWARTZ SURGERY 8TH EDN PG 725
a. A definite diagnosis of tuberculous pleural effusion (TPE. can be difficult to make because of the low sensitivity and/or specificity of noninvasive traditional diagnostic tools.
b. In most series of patients with TPE, the results of pleural fluid staining for acid-fast bacilli are virtually always negative, and pleural fluid cultures are positive for mycobacteria in < 25% of cases.
c. On the other hand, a pleural biopsy specimen will demonstrate granulomatous pleuritis in 80% of patients with TPE, and when a culture of a biopsy specimen is combined with histologic examination, the diagnosis can be established in approximately 90% of cases.
d. The levels of adenosine deaminase (ADA., an enzyme found in most cells, are increased in tuberculous pleural effusions.
e. This determination has acquired popularity as a diagnostic test in high-incidence areas for TPE because it is not invasive, the assay is not expensive, and it is readily accessible.
f. ADA is involved in the proliferation and differentiation of lymphocytes, especially T lymphocytes.
g. They release ADA when stimulated in the presence of live intracellular microorganisms.
h. For this reason, ADA has been looked on as a marker of cell-mediated immunity and, in particular, as a marker of the activation of T lymphocytes.
i. Elevated pleural fluid ADA level predicts tuberculous pleuritis with a sensitivity of 90 to 100% and a specificity of 89 to 100%.
j. Cutoff value for ADA varies from 47 to 60 U/L Specificity is increased when the lymphocyte/neutrophil ratio in the pleural fluid (of > 0.75) is considered together with an ADA concentration of > 50 U/L.