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

Abstract

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

Design and methods: 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.

Results: 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.

Conclusions: 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.