SAAG separates portal hypertension from everything else
Mnemonic
SAAG = serum albumin - ascitic albumin, and “11 is the number”:
- 11 g/l or more means portal hypertension: cirrhosis, heart failure, Budd-Chiari
- Under 11 g/l means not portal hypertension: peritoneal malignancy, tuberculous peritonitis, pancreatitis, nephrotic syndrome
“High gradient, high portal pressure”, which is counterintuitive until you remember the gradient reflects oncotic pressure holding fluid in the vessel against a high hydrostatic pressure.
“250 is the number for infection”: an ascitic neutrophil count of 250 cells per cubic millimetre or more diagnoses spontaneous bacterial peritonitis, regardless of culture, and treatment must not wait for the culture.
Spontaneous bacterial peritonitis is monomicrobial; a polymicrobial growth with a high protein suggests secondary peritonitis from a perforated viscus and needs surgery.
Expansion
Serum ascites albumin gradient = serum albumin - ascitic albumin
| SAAG | Meaning | Causes |
|---|---|---|
| 11 g/l or more | Portal hypertension | Cirrhosis, heart failure, Budd-Chiari, portal vein thrombosis, alcoholic hepatitis, massive hepatic metastases |
| Under 11 g/l | Not portal hypertension | Peritoneal malignancy, tuberculous peritonitis, pancreatitis, nephrotic syndrome, serositis |
The SAAG has replaced the older exudate and transudate classification for ascites because it is far more accurate, at about 97 per cent.
Spontaneous bacterial peritonitis
- Neutrophil count 250 cells per cubic millimetre or more is diagnostic, regardless of culture, and treatment must not wait for the culture
- Culture is positive in only about half, and yield improves markedly if fluid is inoculated into blood culture bottles at the bedside
- Monomicrobial, usually Escherichia coli, Klebsiella or streptococci. A polymicrobial growth with a high protein suggests secondary peritonitis from a perforated viscus, which needs surgery, not antibiotics alone
- It may present with nothing more than encephalopathy, renal impairment or a general deterioration, so a diagnostic tap is indicated in every cirrhotic admission with ascites
Other tests: cytology for malignancy, amylase for pancreatic ascites, triglycerides for chylous ascites, and adenosine deaminase or mycobacterial culture for tuberculosis.
Albumin cover of 8 g per litre removed is given for large volume paracentesis over 5 litres, to prevent post-paracentesis circulatory dysfunction.