SHORT REPORT

New criteria for the differentiation between transudates and exudates

N S Paramothayan¹ and J Barron²

¹ Department of Respiratory Medicine, St Helier Hospital, Carshalton, Surrey SM5 1AA, UK
² Department of Chemical Pathology and Metabolism, St Helier Hospital

Correspondence to:
Correspondence to:
Dr Barron, Department of Chemical Pathology and Metabolism, St Helier Hospital, Carshalton, Surrey SM5 1AA, UK;
jbarron{at}sthelier.sghms.ac.uk

Aims: To investigate whether cholesterol and lactate dehydrogenase (LDH) measurements in fluids are more sensitive and specific markers for differentiating between exudates and transudates, as confirmed clinically, than the measurement of fluid total protein concentrations alone.

Patients/Methods: Serum, pleural fluid, and ascitic fluid from 61 unselected patients were analysed retrospectively for LDH, cholesterol, and total protein. Clinical classification of transudate or exudate was reached independently by reviewing clinical details and laboratory data.

Results: Of 54 samples (40 pleural fluid and 14 ascitic fluid), 30 were classified clinically as exudates and 24 as transudates. Fluid LDH and fluid to serum protein ratio measurements were equally good at differentiating between exudates and transudates, with a sensitivity of 90%, a specificity of 79%, a positive predictive value (PPV) of 84%, and a negative predictive value (NPV) of 86%. A combination of these parameters improved sensitivity to 100% and NPV to 100%, but lowered the specificity to 71% and PPV to 81%. This combination achieved a higher efficiency than Light's criteria.

Conclusion: Routine measurement of fluid LDH values and the calculation of fluid to serum total protein ratios will aid in differentiating exudates from transudates.

Keywords: transudates; exudates; lactate dehydrogenase; cholesterol; total protein

Abbreviations: CCF, congestive cardiac failure; LDH, lactate dehydrogenase; NPV, negative predictive value; PPV, positive predictive value; ROC, receiver operating characteristic

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