Pleural Fluid Cholesterol and Lactate Dehydrogenase for Separating Exudates From Transudates

Abstract

To the EditorTable 1Number and Percentage of Pleural Effusions Misclassified by Each ParameterParameter*PF=pleural fluid; S=serum.Transudates (n=40)Exudates (n=153)Total (n=193)Light's criteria (%)10 (25)3 (2)13 (7)PF cholesterol ≥50 mg/dL (%)3 (7)14 (9)17 (9)PF/S cholesterol ≥0.30 (%)1 (2)11 (7)12 (6)PF LDH and/or6 (15)7 (5)13 (7)cholesterol (%)* PF=pleural fluid; S=serum. Open table in a new tab The study by Costa and colleagues (November 1995)1Costa M Quiroga T Cruz E. Measurement of pleural fluid cholesterol and lactate dehydrogenase: a simple and accurate set of indicators for separating exudates from transudates.Chest. 1995; 108: 1260-1263Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar concluded that measurements of pleural fluid cholesterol and lactate dehydrogenase (LDH) distinguished exudates from transudates with higher specificity than the criteria by Light et al,2Light RW MacGregor MI Luchsinger PC et al.Pleural effusions: the diagnostic separation of transudates and exudates.Ann Intern Med. 1972; 77: 507-513Crossref PubMed Scopus (1204) Google Scholar with the advantages of not requiring a simultaneous blood sample and of a lower cost. A pleural effusion was considered an exudate when LDH was >200 IU/L and/or cholesterol >45 mg/dL in pleural fluid. We have reproduced this analysis in our series of 193 patients diagnosed with pleurisy who were studied in our two hospitals (55 other patients were excluded: 45 had presumptive diagnosis or had more than 1 cause; 6 had empyema; 2 had hemothorax; and 2 had incomplete biochemical data). Forty were classified as having transudates (28 due to congestive heart failure, 7 liver disease, 4 nephrosis or hypoalbuminemia, and 1 urinothorax); and 153 were classified as having exudates (74 due to malignancy, 32 due to tuberculosis, 31 parapneumonic, and 16 other causes). We used a cutoff level of LDH greater than two thirds of the upper limit in the serum, as is proposed by Light,3Light RW Pleural diseases. 3rd ed. Williams & Wilkins, Baltimore1995: 38-39Google Scholar because the normal range was different in each hospital. The best results with the pleural fluid cholesterol level was for a cutoff point of ≥50 mg/dL. When we used an LDH level of >200 IU/L and/or a cholesterol level of >45 mg/dL the results were poorer. Table 1 details the patients misclassified by each parameter. The combination of LDH and/or cholesterol was not superior to Light's criteria. We can argue that this combination has a lower cost, but also it was not significantly superior to the pleural fluid cholesterol level alone (McNemar's test). In the study of Costa et al1Costa M Quiroga T Cruz E. Measurement of pleural fluid cholesterol and lactate dehydrogenase: a simple and accurate set of indicators for separating exudates from transudates.Chest. 1995; 108: 1260-1263Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar 180 patients were analyzed, but there was a high number of excluded cases (371 and 108 of them because the diagnosis was considered presumptive or the patient had more than 1 disease). It is possible that this fact influenced the results by selecting the more obvious cases. Unfortunately, we have been unable to confirm in our patients the interesting results of Costa et al.1Costa M Quiroga T Cruz E. Measurement of pleural fluid cholesterol and lactate dehydrogenase: a simple and accurate set of indicators for separating exudates from transudates.Chest. 1995; 108: 1260-1263Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar