Ascitic fluid interpretation [advanced]

Appearances

• Straw: serous effusion (clear = transudate; cloudy = exudates)
• Bloody: trauma, malignancy, haemorrhagic pancreatitis, perforated peptic ulcer
• Turbid: SBP, perforated viscus
• Chylous (milky): malignancy, lymphoma, tuberculosis, parasitic

Serum-ascites albumin gradient (SAAG)

The SAAG indirectly measures portal pressure and can be used to determine if ascites are due to portal hypertension:

SAAG= serum albumin – ascitic fluid albumin

NOTE: ensure all values are in g/L

High SAAG >11g/L causes = PORTAL HYPERTENSION

• Portal hypertension causes
  • Pre-hepatic: portal vein thrombosis
  • Hepatic: cirrhosis, chronic hepatitis
  • Post-hepatic: right heart failure, constrictive pericarditis, Budd-Chiari syndrome

Low SAAG <11g/L causes = OTHER

• Other causes
  • Peritoneal disease: intra-abdominal malignancy, peritoneal dialysis, TB
  • Hypoalbuminaemia: nephrotic syndrome, malnutrition, protein-loosing enteropathy
  • Other: pancreatitis/pancreatic pseudocyst, haemoperitoneum, myxoedema, chylous ascites

Cell count and differential

Neutrophils >0.25×10⁹/L = spontaneous bacterial peritonitis

Other units: >250×10⁶/L; >250cells/cumm; >250cells/µL

If the laboratory does not differentiate types of white cells, a WCC of >0.5×10⁹/L may be used instead

Other tests

• Cells
  • MC&S: identify infective causes
  • Cell count
    • Neutrophils (normally <0.25×10⁹): raised in spontaneous bacterial peritonitis
    • Lymphocytes (normally <0.5x 10⁹): raised in inflammation, TB, malignancy
  • Cytology: identify malignant causes
• Tests for transudate vs exudates – largely replaced by SAAG
  • Protein (<25g/L = transudate; >25g/L = exudate)
  • LDH (<225U/L = transudate; >225U/L = exudate)
• Other tests to consider
  • Amylase (normally similar to serum levels): raised in pancreatitis/pancreatic pseudocyst/pancreatic trauma
  • Glucose (normally similar to serum levels): decreased in TB and malignancy