Objectives and background: The determination of adenosine deaminase (ADA) activity in pleural fluid is important for differentiation of pleural effusions and diagnosing pleural tuberculosis. Although measurement of ADA is simple and inexpensive, controversies exist regarding potential errors caused by time elapsed between sample collection and analysis, storage temperature and the use of anticoagulants. The objective of this study was to evaluate the influence of storage time (1, 3, 7, 10 and 28 days) and temperature (4 degrees C and -20 degrees C) on the determination of ADA in pleural fluid samples collected in EDTA and sent at ambient temperature to the laboratory for initial processing within 1 h of collection.
Methodology: Twenty-seven pleural exudates obtained from 20 patients with neoplastic disease and seven with tuberculosis were analysed. The ADA activity obtained within 1 h of collection was considered the gold standard and was compared with the other measurements.
Results: The correlation between the initial measurement and all others was >or=0.90 for both temperatures up to the 10th day after thoracocentesis and tended to decrease by 28 days after collection, but this difference was not significant.
Conclusions: Pleural fluid samples collected in EDTA and sent for analysis within 1 h after collection can be used to determine ADA up to 28 days after collection if stored at 4 degrees C or -20 degrees C, with no evidence of significant increases or decrease in enzyme activity that might distort the results.