Soluble leukocyte selectin in the analysis of pleural effusions

Can cholesterol be used to distinguish pleural exudates from transudates? evidence from a bivariate meta-analysis

Background

Many studies have investigated whether pleural cholesterol levels can aid in diagnosis of pleural exudates, and the results have varied considerably. To gain a more reliable answer to this question, we meta-analyzed the literature on using pleural cholesterol or the ratio of cholesterol in pleural fluid to cholesterol in serum (P/S cholesterol ratio) as diagnostic tests to help identify pleural exudates.

Methods

Literature databases were systematically searched for studies examining accuracy of pleural cholesterol or P/S cholesterol ratios for diagnosing pleural exudates. Data on sensitivity, specificity, positive/negative likelihood ratio (PLR/NLR), and diagnostic odds ratio (DOR) were pooled using bivariate-effects models. Summary receiver operating characteristic (SROC) curves and area under the curve (AUC) were used to summarize overall test performance.

Results

Our meta-analysis included up to 20 studies involving 3,496 subjects. Summary estimates for pleural cholesterol in the diagnosis of pleural exudates were as follows: sensitivity, 0.88 (95%CI 0.84 to 0.92); specificity, 0.96 (95% CI 0.92 to 0.98); PLR, 20.31 (95% CI 11.21 to 36.78); NLR, 0.12 (95% CI 0.09 to 0.17); DOR, 167.06 (95% CI 76.79 to 363.95); and AUC 0.97 (95% CI 0.95 to 0.98). The corresponding summary performance estimates for using the P/S cholesterol ratio were as follows: sensitivity, 0.94 (95% CI 0.92 to 0.96); specificity, 0.87 (95% CI 0.83 to 0.91); PLR 7.46 (95% CI, 5.47 to 10.19); NLR, 0.07 (95% CI 0.05 to 0.10); DOR, 107.74 (95% CI 60.91 to 190.60); and AUC 0.97 (95% CI 0.95 to 0.98).

Conclusions

Both pleural cholesterol level and the P/S cholesterol ratio are helpful for the diagnosis of pleural exudates. Nevertheless, the results of pleural cholesterol assays should be interpreted in parallel with the results of traditional tests and clinical information.

The Light criteria: the beginning and why they are useful 40 years later

The Light criteria serve as a good starting point in the separation of transudates from exudates. The Light criteria misclassify about 25% of transudates as exudates, and most of these patients are on diuretics. If a patient is thought likely to have a disease that produces a transudative pleural effusion but the Light criteria suggest an exudate by only a small margin, the serum-pleural fluid protein gradient should be examined.

Is it meaningful to use biochemical parameters to discriminate between transudative and exudative pleural effusions?

OBJECTIVES

The usefulness of biochemical criteria to separate pleural transudates from exudates is controversial, and the limitations of Light's criteria in patients receiving diuretic therapy is of general concern. We evaluated the added value of biochemical criteria to clinical judgment for separating transudates from exudates.

SETTING

A community teaching hospital.

DESIGN

A prospective, observational study for the evaluation of diagnostic tests.

PATIENTS AND MEASUREMENTS

In 249 consecutive patients referred for diagnostic thoracentesis, two physicians classified the pleural effusion as transudate or exudate based on all available information just before performing the thoracentesis. The sensitivity, specificity, and accuracy of the clinical presumption were compared with those of Light's criteria, and serum-pleural fluid albumin and protein gradients. The combined accuracy of biochemical and clinical criteria was also assessed.

RESULTS

The accuracy of Light's criteria (93%) was significantly higher than that showed by the initial clinical presumption (84%; p < 0.01) and that of the alternative biochemical criteria: serum-pleural fluid albumin gradient (87%; p < 0.03) and serum-pleural fluid protein gradient (86%; p < 0.01). In patients receiving diuretic therapy, the accuracy of Light's criteria was 83% (60 of 72 cases), neither different to that of the albumin gradient (88%; 63 of 72 cases) nor to that of the protein gradient (86%; 62 of 72 cases). When these alternative biochemical criteria were applied exclusively to patients receiving diuretics who were thought to have a transudative effusion by clinical criteria, but having fluid identified as exudative by Light's criteria, the results did not improve significantly. Using a multiparametric model for the population receiving diuretics, the accuracy was greater (93%; 67 of 72 cases) than that of Light's criteria but without reaching statistical significance (p = 0.12).

CONCLUSIONS

Light's criteria are significantly superior to the clinical presumption to separate pleural transudates from exudates. In patients receiving diuretics, Light's criteria lose accuracy, which is similar to that showed by the use of alternative biochemical criteria alone or combined with clinical judgment.