Biochemical analysis of ascitic (peritoneal) fluid: what should we measure?

Ascitic fluid samples are frequently sent to the laboratory for analysis. Although the underlying cause of the ascites is often thought to be clinically obvious, it is important to establish a definitive diagnosis. The value of a cell count and bacterial culture of the ascitic fluid is not disputed, but the role of biochemical testing is less clear. The use of ascitic fluid total protein to try to classify ascitic fluids as either an exudate or a transudate has contributed to this. The use of the physiologically based serum ascites albumin gradient to differentiate ascites caused by portal hypertension from other causes provides a better diagnostic approach. We recommend that the serum ascites albumin gradient is performed by laboratories as the first-line test and that interpretative reports are provided. Additional testing should be restricted to specific diagnostic queries and requires close collaboration between the laboratory and the clinician.