IBMS Congress

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Clinical Utility of Fluid Protein Measurement

Fluid Proteins

Clinical Chemistry

Dr Ruth Lapworth, William Harvey Hospital

Pleural effusions and ascites are common medical problems with a wide variety of causes. In many instances, pleural and ascitic fluid samples are sent to the laboratory for analysis when the fluid has been aspirated for therapeutic rather than diagnostic reasons. 

It is important therefore that any biochemical testing is directed at answering a specific clinical question rather than the laboratory performing all the tests that may be requested on a particular fluid sample.

Traditionally, pleural fluids have been classified based on the underlying pathophysiology as either exudative or transudative effusions. Modification of Light’s criteria, and their use in less well defined populations to discriminate exudates from transudates has resulted in lower diagnostic accuracy than was originally reported.  Publication of Guidelines for the investigation of a unilateral pleural effusion in adults has rekindled interest in this area.  However, in many cases measurement of pleural fluid total protein is the only test necessary for classification of pleural effusions.

The physiological processes leading to the accumulation of ascitic fluid differ from those involved in pleural fluid formation. The exudate/transudate concept has been widely used in the differential diagnosis of ascites but in this context the concept is flawed and can give misleading information.  Ascitic fluid total protein measurement is of limited value and should be replaced with the serum ascites albumin gradient (SAAG) which reflects the presence of portal hypertension.