Optimising the utility of pleural fluid adenosine deaminase for the diagnosis of tuberculous pleural effusion

Introduction: Pleural fluid adenosine deaminase (pfADA) is a simple, rapid and inexpensive surrogate marker for tuberculous pleural effusion (TPE). A nationwide cut-off of 40 U/L is currently used based on overseas data. There is a need to optimise the diagnostic utility of pfADA by establishing a local cut-off value. In this study, we aimed to describe the demographics and clinical characteristics of patients with TPE and non-TPE; determine the sensitivity and specificity of current pfADA of 40 U/L; and establish a new local pfADA cut-off for TPE. Methods: We conducted a single-centre, observational, prospective study of patients with exudative pleural effusion and pfADA measured from 1 October 2019 to 30 April 2020 at Queen Elizabeth Hospital, Malaysia. Results: The diagnosis of analysed patients (n = 93) included TPE (n = 41), malignancy (n = 28), parapneumonic effusion (n = 12) and other causes (n = 12). The mean pfADA was 51.15 U/L (standard deviation (SD) = 13.77) among TPE group and 18.86 U/L (SD = 12.33) among non-TPE. When analysis was restricted to TPE patients, the local pfADA cut-off is 29.6 U/L, with a sensitivity of 97.6% and specificity of 90.4%. The current pfADA of 40 U/L has a sensitivity of 87.8% and specificity of 92.3%. Conclusion: We established a local pfADA cut-off of 29.6 U/L for TPE. Optimising the utility of pfADA helps to enhance clinicians' treatment confidence of TPE when initial work-up is inconclusive.