Pleural fluid protein is inversely correlated with age in uncomplicated parapneumonic pleural effusions

Assess whether age influences standard biochemical parameters used in the differential diagnosis of transudative and exudative pleural effusions.

We retrospectively analyzed data from the database of our clinic from 225 patients with pleural effusions categorized based on their final diagnosis in 5 groups: transudates 41 (18%), uncomplicated parapneumonic 26 (12%), complicated parapneumonic 20 (9%), tuberculosis 35 (15%) and lung cancer 103 (46%). We tested whether age correlated with pleural fluid protein or lactate dehydrogenase.

There was a statistically significant inverse correlation only between the age and the pleural fluid protein content in patients with uncomplicated parapneumonic effusions with correlation coefficient r=-0.6 [(95% CI=-0.8 to -0.28); p=0.001]. Linear regression analysis showed that this association is given by the equation: age=101.998-10.03 protein. In the same group of patients age was not correlated with serum protein content.

Our study shows that age may be a confounding factor in the differential diagnosis of transudative and exudative pleural effusions. Clinicians should be aware of this finding especially when dealing with elders.