Ascitic Fluid Biochemical Analysis

Function

Ascitic fluid biochemical analysis involves the laboratory evaluation of fluid accumulated within the peritoneal cavity (ascites). The primary goal is to determine the underlying cause of fluid accumulation, which usually involves measuring albumin, total protein, glucose, and lactate dehydrogenase (LDH).

Why it is Ordered

This test is essential for patients presenting with new-onset ascites or those with known ascites who experience clinical deterioration (e.g., fever, abdominal pain). It helps differentiate between causes related to portal hypertension (like cirrhosis) and those not related (like malignancy or infection).

The SAAG Score

The Serum-Ascites Albumin Gradient (SAAG) is the most useful calculation derived from this analysis. It is calculated by subtracting the ascitic fluid albumin concentration from the serum albumin concentration measured on the same day.

• High SAAG (≥ 1.1 g/dL): Indicates portal hypertension, common in cirrhosis, alcoholic hepatitis, and congestive heart failure.
• Low SAAG (< 1.1 g/dL): Suggests causes other than portal hypertension, such as peritoneal carcinomatosis, tuberculosis, or nephrotic syndrome.

Associated Conditions

• Spontaneous Bacterial Peritonitis (SBP): Characterized by a high neutrophil count in the fluid.
• Cirrhosis: The most common cause of ascites in the Western world.
• Pancreatitis: Suggested by high levels of amylase in the fluid.