When pleural potassium exceeds 5.0 mEq/L, high pleural adenosine deaminase levels do not necessarily indicate tuberculous pleuritis

The aim of this study was to determine whether high levels of pleural adenosine deaminase (pADA) are predictive for tuberculosis when pleural effusions do not satisfy the criteria for lymphocytic effusions or show neutrophil predominance.

This was a retrospective observational study of 147 consecutive patients with exudative pleural effusions that were diagnosed by analysis of fluid samples during a 3-year period from 1 April 2007 to 31 March 2010. Multiple linear correlation tests were used to assess clinical variables as possible predictors of high pADA levels.

High pleural LDH (pLDH) and pleural potassium (pK) levels were associated with high pADA levels (P < 0.0001). Although there was a linear correlation between pLDH and pADA levels in patients with parapneumonic effusions (PPE) (n = 75), tubercular effusions (n = 21), malignant effusions (n = 41) and miscellaneous effusions (n = 10), a significant linear correlation between pK and pADA levels was observed only in patients with PPE (ρ = 0.525, P < 0.0001). When the cut-off value for pK was set at 5.0 mEq/L, pADA levels were >50 IU/L and pK levels were >5.0 mEq/L in only one patient (5%) in the tuberculosis group (n = 21) and 15 patients (12%, all with PPE) in the non-tuberculosis group (n = 126).

When pK levels exceed 5.0 mEq/L, high pADA levels do not necessarily indicate the presence of tuberculous pleuritis.