A comparative analysis of biochemical parameters in exudative and transudative pleural fluids using different criterias: a study in a tertiary care centre

Pleural effusion is a common clinical problem resulting from thoracic or systemic diseases. Several biochemical parameters, serological and cytological markers are used to classify the type of pleural effusion. The oldest classification is Light's criteria which categorizes exudates by meeting one of these criteria: Pleural to serum protein ratio> 0.5, pleural to serum LDH ratio> 0.6 and isolated LDH > two third of normal upper limit of serum LDH. Others criteria are protein gradient and Serum effusion albumin gradient. Combination of clinical findings along with biochemical findings along with cytology helps in determining the etiology of pleural effusion.

One hundred fifty samples of pleural fluid paired with serum were examined. Pleural fluids were also subjected to biochemical study to find out the level of protein, albumin, glucose, Adenosine deaminase levels, LDH, total and differential cell counts, Gram's stain and Modified Ziehl-Neelsen stain. Serum samples were evaluated for protein, albumin and LDH levels.

Out of 250 samples, total of 71.2% samples were exudative and 28.8% were transudative. There were 184 males and 66 females. Tuberculosis (42.7%) followed by para-pneumonic effusion (22%) was commonest etiology seen in exudative pleural effusions. In transudates, chronic liver disease (10.8%) followed by chronic renal disease (8.4%) was the commonest etiologies encountered. Light's criteria was nearly successful in classifying all exudates. All the inflammatory effusions were 100% classified by pleural LDH levels. All transudates are correctly classified by Serum effusion albumin gradient.

Light's criteria was most sensitive in identifying exudates but not specific in cases of transudates specially heart failure patients. Light's criteria was 97.7% successful in classifying exudative pleural effusion. Combination of pleural LDH and pleural fluid to serum protein ratio was successful in classify all the exudates correctly.