ACCS Practice Exam 2026 – Complete Test Preparation Guide

The diagnostic finding that is primarily used to distinguish between exudate and transudate in pleural effusion is the measurement of protein levels in the pleural fluid. The Light's criteria are commonly applied in this context, which include comparing the pleural fluid protein concentration to the serum protein concentration. If the pleural fluid protein is greater than 0.5 times the serum protein or if the pleural fluid lactate dehydrogenase (LDH) level is greater than 0.6 times the serum LDH, the effusion is classified as an exudate. Exudative effusions typically indicate underlying inflammatory, malignancy, or infectious processes, while transudative effusions are usually associated with systemic conditions such as heart failure or cirrhosis.

Although lateral decubitus radiographs, amylase levels, and pH can provide valuable information regarding pleural effusions and other pleural pathologies, they are not the primary factors used for this distinction between exudate and transudate. In particular, while pH can help assess the type of effusion (especially in cases of empyema), it is not a baseline criterion like protein is for the purpose of differentiation. Consequently, understanding the