Evaluation of the applicability of Light’s criteria for differentiation of transudates from exudates across different serous fluids

Background: Serous fluids like pericardial, pleural and ascitic fluids are frequently submitted for pathological evaluation. The differentiation of these fluids into transudates and exudates is the prime aim of the evaluation as this determines the patients’ further management. Light’s criteria, proposed about 50 years ago, utilize various biochemical parameters for this differentiation and are the most widely used criteria. Materials and Methods: This study was carried-out in Pathology department of Punjab Institute of Cardiology, Lahore. 60 serous fluid samples, including pericardial, pleural and ascitic fluids were analyzed routinely and classified into transudates and exudates applying Light’s criteria. The proportion of transudates and exudates were compared amongst different fluids by applying chi-square test, keeping level of significance at p-value <0.05. Cytological examination was reported according to the International System for Reporting Serous Fluid Cytopathology. Results: Most of the fluids, i.e., 44 out of 60 were exudates. This trend was most pronounced for pericardial fluids where 29 out of 31 were exudates. 13 pleural fluids out of 23 were exudative while only 2 out of 6 ascitic fluids were exudative. On cytological examination, 55 fluids were negative for malignant cells, 2 fluids harbored atypical cells and 3 were positive for malignant cells. Careful gross examination of fluids furnished vital information in many cases. Conclusion: Light’s criteria may not be equally applicable across all types of fluids. In our study it had a high sensitivity but low specificity for pericardial exudates. Hence, modification of the criteria may be required to enhance its validity. Careful gross and cytological examination may provide additional invaluable information that could significantly impact management strategies. Keywords:  Pleural fluid, pericardial fluid, light’s criteria, transudate, exudate.