Characteristics of pleural effusions associated with pulmonary embolism.

Pleural fluid characteristics were analyzed in 26 patients with pulmonary embolism. All determinations were highly variable. A bloody effusion occurred in 65%, while clear fluid was found in 35%. White blood cell counts had a wide distribution of values; polymorphonuclear leukocytes predominated in 61% and lymphocytes in 39%. Less than two thirds of tested specimens were exudates by standard criteria. Only 27% of effusions had the "typical" pattern of bloody appearance, polymorphonuclear predominance, and characteristics of an exudate. Roentgenographically evident infiltrates occurred in 62% and were correlated with bloody pleural fluid (P less than .01), which suggests that infarction is not necessary for effusion to occur, but may account for a bloody appearance. The variability of these results indicates that there are no typical or diagnostic pleural fluid findings in pulmonary embolism.