D-dimer is a degradation product of cross-linked fibrin. We hypothesized that hemorrhagic pleural effusions would have greater D-dimer levels than non-hemorrhagic pleural effusions, and that persistently bloody effusions would be distinguishable from thoracentesis-induced bloody effusions by the D-dimer level.

Forty pleural effusions were studied. D-dimer levels (measured by ELISA), red blood cell (RBC) count, white blood cell (WBC) count, lactate dehydrogenase (LDH), and protein level was measured for each effusion. Ten effusions, five non-bloody, and five bloody were studied for each of the following disease states: parapneumonic effusion, congestive heart failure, post-coronary artery bypass grafting, and lung cancer.

No significant difference of the D-dimer level was noted between bloody and non-bloody effusions of different disease states ( ). There was no significant difference in the median D-dimer levels between all the bloody and all the non-bloody effusions ( ). There was no significant difference ( ) in D-dimer levels between five diseases groups when the bloody and non-bloody fluids were combined. The D-dimer levels did not correlate with the RBC count ( ,  ), WBC count ( ,  ), LDH ( ,  ), or protein levels ( ,  ) in any of the groups.

Measurement of pleural fluid D-dimer levels does not distinguish persistently bloody effusions from non-bloody effusions, and does not aid in narrowing the differential diagnosis of an effusion.