[Value of determining the activity of adenosine deaminase (ADA) in the differential diagnosis of pleural effusions].

Background: Pleural effusion (PE) is a common problem in medical practice. Transudative effusions usually do not present difficulty in diagnosis, in most populations. Exudative PE however, require careful differential diagnosis that include necessarily tuberculosis and metastatic cancer.
Methods: We have conducted a cross-sectional study of 221 patients with persistent PE, in order to evaluate accuracy of determining adenosine deaminase activity (ADA) for diagnosis of tuberculosis pleuritis. This group of patients, taken mostly from the State Hospital for pulmonary diseases, consecutively, was constituted as follows: 1) Tuberculosis (confirmed, n = 150; likely, n = 9); 2) Cancer (confirmed, n = 21; likely, n = 16; Lymphoma = 3); and 3) Miscellaneous (n = 22). All individuals were submitted to clinical examination, chest X-ray, blood tests, and underwent thoracocentesis with pleural biopsy. Pleural fluids were analyzed by routine tests plus determination of ADA activity using Giusti's Method.
Results: In agreement with previous reports we have found 40 U/L to be the best cutoff point according to a Receiver Operating Curve (ROC) analysis of our data. Sensitivity of ADA activity < or = 40 U/L was 93.3% and specificity 93.5%, resulting in a positive predictive value of 97.2% and a negative predictive value of 85.3%, in this specific population of patients, when taking into account only the individuals with confirmed tuberculosis by histopathology or culture. Three out of the 4 patients with elevated ADA without tuberculosis had lymphoma.
Conclusion: ADA determination in pleural fluids, a quick and inexpensive technique, is shown to be an accurate method for identifying tuberculosis pleuritis. Our findings are comparable to reports from other series, and stress how useful it is to incorporate this test to the routine evaluation of pleural effusions in areas of high incidence of tuberculosis.