Analysis od less common body fluids: Part 2 –⁠ peritoneal fluid and ascites

Overview

This report provides an overview of the pathophysiology and clinical biochemistry of peritoneal fluid and the diagnostic importance of ascitic fluid analysis in diseases associated with ascites formation. Pathophysiology: Peritoneal fluid is normally present in small amounts within the peritoneal cavity; a pathological increase above 500 mL is classified as ascites. The main mechanisms of ascites formation include portal hypertension, increased venous pressure, changes in capillary permeability, splanchnic vasodilation, impaired oncotic pressure, and lymphatic obstruction. The condition is further complicated by systemic compensatory vasodilation, which leads to increased portal flow, bacterial translocation from the gut, and subsequent activation of the immune system. Types of effusions: Instead of the traditional classification into transudates and exudates, classification based on the serum-ascites albumin gradient (SAAG -⁠ the difference between serum and ascitic albumin concentrations) is recommended. A SAAG value of ≥11 g/L indicates portal hypertension, while values <11 g/L suggest malignancy or peritoneal inflammation and infections. Further differentiation can be made using total protein concentration in the ascitic fluid. Clinical conditions with peritoneal effusions: The main causes of ascites include cirrhosis (particularly alcohol-related), malignancies, heart failure (especially right-sided), nephrotic syndrome, and chronic kidney disease. Laboratory analysis: In addition to macroscopic examination, the primary diagnostic tool in clinical biochemistry is the serum-ascites albumin gradient (SAAG). Other parameters analyzed in ascitic fluid include protein, glucose, LDH, cholesterol, and triglycerides. Amylase, alkaline phosphatase, CEA (or other tumor markers), and adenosine deaminase (in tuberculous peritonitis) may also be diagnostically useful. For diagnosing spontaneous bacterial peritonitis, the key measurement is the white blood cell and neutrophil count in ascitic fluid.

Conclusion: The severity of conditions associated with ascites necessitates laboratory testing of both ascitic fluid and blood, and in some cases, other body fluids as well.

Keywords:

Cirrhosis – Ascites – peritoneal fluid – serum-to-ascites albumin gradient (SAAG)