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

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

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

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

Fluids