Effect of iatrogenic haemorrhage on biochemical parameters in pleural effusions

Pleural fluid (PF) samples may become haemorrhagic due to trauma during diagnostic procedures. We aimed to evaluate the effect of increasing blood concentrations in pleural fluids on biochemical parameters which are used to discriminate transudates and exudates.

Sixty-seven pleural fluid samples were separated into five test tubes. Patient's own blood was added in the test tubes in different concentrations as follows: No blood in the first tube, 2% in the 2nd, 5% in the 3rd, 10% in the 4th, 20% in the 5th tube.

After addition of blood, statistically significant changes in all biochemical parameters in transudate groups were detected. The characteristics changed from transudate to exudate 12.9%, 14%, 11.4%, 27% and 14.3% according to Light's criteria, serum-PF albumin gradient, cholesterol level, PF/serum cholesterol and PF/serum bilirubin, respectively. Results indicating an exudate according to Light's criteria were evident only in the 5th tube group, however, when other biochemical parameters were used, classification of samples could be altered with lower concentrations of blood.

Contamination of blood, especially in borderline transudative pleural effusions, may result in misclassification as an exudate. Light's criteria appear to be the least effected and therefore the most reliable parameters in bloody effusions.