Evaluation of cholinesterase to differentiate pleural exudates and transudates

The present study was undertaken to evaluate the usefulness of pleural fluid cholinesterase (PChE) level in pleural fluid and its ratio to serum cholinesterase (P/SChE) in order to differentiate transudates and exudates and to compare their diagnostic efficacy with the Light's criteria.

A total of 110 patients of pleural effusion of diverse etiology were studied. Eighty patients were of exudative pleural effusion of tubercular, malignant or parapneumonic origin and 30 patients were of transudative effusion. Cholinesterase was estimated in the pleural fluid and serum in all the patients.

The mean PChE and P/S ChE were significantly higher in exudates as compared to transudates (p < 0.001). P/S ChE was 0.79 +/- 0.45 and 0.14 +/- 0.11 in exudates and transudates, respectively. When a cut-off value of 469 IU/L for PChE was taken for the diagnosis, it was found that 10% of exudates and 2.5% of transudates were misclassified. However percentage of misclassification decreased to 1.25% in exudates and 3.3% in transudates when the cut-off value of 0.24 for P/S ChE ratio was used. Using Light's criteria, a sensitivity of 91.25% and specificity of 90% with positive predictive value (PPV) of 96.05% and negative predictive value (NPV) of 79.42% was observed. However using P/S ChE, the PPV was 98.75% and NPV was 96.67%.

The estimation of PChE and P/SChE ratio had better discriminatory capacity than Light's criteria. It is cost effective and more specific, therefore its routine estimation is recommended.