High pleural fluid adenosine deaminase levels: a valuable tool for rapid diagnosis of pleural TB in a middle-income country with a high TB/HIV burden.

Abstract

South Africa has the highest burden of tuberculosis (TB) in the World Health Organization (WHO) African region. Using traditional TB diagnostic tools, the diagnosis of pleural TB (PTB) is highly unrewarding. Elevated levels of pleural fluid adenosine deaminase (FADA) have been shown to be useful in the diagnosis of PTB; however, similar levels may be found in some other medical conditions leading to misdiagnosis. Following queries from clinicians concerning the likely high false-positive (FP) rate of FADA from our laboratory, we performed a retrospective audit of all high FADA results generated over a 12-month period. To determine the positive predictive value (PPV) of FADA, the frequent causes of FPs in our laboratory and the demographic characteristics of tuberculous pleural effusions (TPEs) and non-tuberculous pleural effusions (NTPEs). High FADA results generated in the past year were extracted with corresponding TB culture results, fluid cell count, cytology/ histology results, radiology reports and HIV results. Hospital records were reviewed for the final diagnosis in each case. Diagnosis of PTB was based on the WHO case definition of TB. A total of 159 results were reviewed: 133 (83.6%) were TPE, hence FADA had a PPV of 83.6%. Neoplasm was the most common cause of an FP in 13/26 (50%) NTPEs. While TPE was more common than NTPE in younger people, both groups had an equal gender distribution. FADA had a high PPV for PTB in our laboratory. We recommend its continued use as a rapid and reliable diagnostic tool for PTB.