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Background: Storing pleural fluid samples for research purposes is a common practice, but whether adenosine deaminase (ADA), an enzyme used for the diagnosis of tuberculous pleuritis, is stable over long periods of time is unknown.
Methods: We evaluated the stability of pleural ADA concentrations in 223 samples frozen at -80ºC as compared to values obtained immediately following the initial thoracentesis. Sample storage time ranged from several months to slightly more than 10 years.
Results: ADA activity was stable for up to 2.6 years. Afterwards, it decreased 6 to 8 U/L, enough to drop 2 (3.3%) tuberculous patients below the diagnostic ADA cutoff.
Conclusions: As far as ADA enzymatic activity is concerned, pleural fluid samples are viable for extended periods of time. However, some caution in interpreting results from specimens stored for > 2.6 years is prudent.
DOI: 10.7754/Clin.Lab.2013.130311
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