History and Objectives: Light’s criteria in which serum and pleural LDH activity and proteins levels are the most common variables to differentiate exudative from transudative pleural effusion, for the past 3 decades. Several other biochemical parameters have been suggested, one of which is serum pleural effusion albumin gradient (>1.2: transudate, <1.2: exudate). The present study was performed to assess diagnostic value serum and pleural gradient in the patient with pleural effusion.

Materials and Methods: A descriptive study was carried out on 76 patients. In a sitting position, pleural fluid aspiration was obtained and albumin, lactate dehydrogenase (LDH), protein level and at the same time blood total protein, LDH and albumin was obtained, on the basis of Light’s criteria, pleural fluid is categorized as exudate or transudate. 76 patients presented with pleural effusion referred to the Shaheed Beheshti hospital (Kashan) were studied according to the Light’s criteria and gradient method.

Results: According to Light’s criteria, 41 patients (54%) had transudate and 35 patients (46%) had exudate. These measures were 59% and 41% respectively in gradient method. Thus discrepancy was noted in 6 cases, labeled exudate according to Light’s criteria however transudate according to gradient method. Sensitivity, specificity, positive and negative predictive value were 82.9%, 95%, 93.5% and 86.6% respectively for gradient method.

Conclusion: Sensitivity of Light’s criteria is higher than albumin gradient, but the gradient method has a higher specificity for patients who are clinically suspect of transudate but labeled exudate according to Light’s criteria, albumin gradient is helpful.