Ascitic fluid interpretation [advanced]

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Diagnostic abdominal paracentesis (ascitic tap) is covered here!


  • 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


  • 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
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