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Analysis of pleural fluid can have, on its own, a high diagnostic value. In addition to thoracocentesis, a diagnostic hypothesis based on medical history, physical examination, blood analysis and imaging tests, the diagnostic effectiveness will significantly increase in order to establish a definite or high probable diagnosis in a substantial number of patients. Differentiating transudates from exudates by the classical Light's criteria helps knowing the pathogenic mechanism resulting in pleural effusion, and it is also useful for differential diagnosis purposes. An increased N-terminal pro-brain natriuretic peptide, both in the fluid and in blood, in a due clinical context, is highly suggestive of heart failure. The presence of an increased inflammatory marker, such as C-reactive protein, together with the presence of over 50% of neutrophils is highly suggestive of parapneumonic pleural effusion. If, in these cases, the pH is<7.20, then the likelihood of complicated pleural effusion is high. There remains to be demonstrated the usefulness of other markers to differentiate complicated from uncomplicated effusions. An adenosine deaminase > 45 U/L and>50% lymphocytes is suggestive of tuberculosis. If a malignant effusion is suspected but the cytological result is negative, increased concentrations of some markers in the pleural fluid can yield high specificity values. Increased levels of mesothelin and fibruline-3 are suggestive of mesothelioma. Immunohistochemical studies can be useful to differentiate reactive mesothelial cells, mesothelioma and metastatic adenocarcinoma. An inadequate use of the information provided by the analysis of pleural fluid would results in a high rate of undiagnosed effusions, which is unacceptable in current clinical practice., (Copyright © 2014 Elsevier España, S.L.U. All rights reserved.)

Background: To analyze the adenosine deaminase (ADA) pleural levels and the possibility of a typical pattern of tuberculous pleuritis (TP) in relation to these values., Patients and Methods: We analyzed 90 consecutive cases of TP dividend into two groups on the basis of the pleural ADA measurements: group 1 (less than 43 U/I) and group 2 (equal or higher than 43 U/I). We compared: age, sex, tuberculous risk factors, clinic onset and duration, PPD, chest roentgenogram, biochemical (LDH, glucose and proteins) and cytological examination of the pleural fluid, microbiologic studies on sputum, pleural fluid and biopsies, histologic findings of the biopsies, evolution and sequelae after the treatment., Results: 36 patients in the group 1 (40%) and 54 in the group 2 (60%) (p = 0.01). All the parameters were similar in both groups excluding LDH pleural levels, that were higher in group 2. In 20 cases of the group 1, we obtained a second analysis of pleural ADA and we observed in 11 cases (55%) an ADA value above 43 U/I., Conclusions: We confirmed that ADA pleural level is increased in the majority of our patients with a low initial sensibility of 60%, that can increase with a second determination (72%). ADA activity below 43 U/I cannot exclude the tuberculous aetiology of an effusion and can persist negative in other analyses. The results suggest a response of different chronology without any relation to initial ADA pleural level.

The concentration of gamma interferon (IFN gamma) and adenosine deaminase (ADA) activity were measured in the pleural fluid of 162 patients to compare their diagnostic significance and to establish a possible correlation between both tests. The IFN gamma levels in tuberculous pleural effusions were quite variable, with a mean of 93 U/ml and a median of 48 U/ml. They were higher than 2 U/ml in all cases, whereas no case of nontuberculous effusion showed higher values. ADA activity was higher than 43 U/l in all tuberculous effusions, with a mean value of 80 U/l, higher than in any other group except lymphoma. In three pleural effusions associated with lymphoma, one with mesothelioma, one with adenocarcinoma and four with empyema, ADA activity was higher than 43 U/l. In these patients, IFN gamma levels were low. There was no correlation in the whole series or in any group between IFN and ADA. Both parameters can be very useful for the diagnosis of tuberculous pleuritis. The measurement of IFN gamma is more specific, although the experience with this test is more limited than with ADA. It has the additional shortcoming of a high cost and it requires facilities for radionuclide use. Therefore, we think that ADA measurement should be considered as a routine test while IFN gamma measurement should be reserved for reference institutions.