SAAG Calculation
The SAAG is 0.7 g/dL (serum albumin 1.8 g/dL minus ascitic fluid albumin 1.1 g/dL), which indicates a low gradient (<1.1 g/dL) and suggests a non-portal hypertension cause of ascites. 1
How to Calculate SAAG
- SAAG is calculated by subtracting the ascitic fluid albumin concentration from the serum albumin concentration measured on the same day 1
- In this case: 1.8 g/dL (serum) - 1.1 g/dL (fluid) = 0.7 g/dL 2
Interpretation of This Result
- A SAAG <1.1 g/dL indicates the absence of portal hypertension as the primary cause of ascites 1
- This low gradient suggests non-portal hypertension etiologies with approximately 97% accuracy 1, 3
Differential Diagnosis for Low SAAG (<1.1 g/dL)
The most common causes to consider include:
- Peritoneal carcinomatosis (malignant ascites without liver metastases) 1, 4
- Tuberculous peritonitis 1, 4
- Nephrotic syndrome 4, 3
- Pancreatic ascites 4
Critical Clinical Caveat
In patients with known cirrhosis who present with a low SAAG, only 38% have an identifiable non-portal hypertension cause 5. The most common identifiable causes in cirrhotic patients with low SAAG are:
- Primary bacterial peritonitis (38% of identifiable causes) 5
- Peritoneal carcinomatosis or malignant ascites (28% of identifiable causes) 5
- Nephrotic syndrome (17% of identifiable causes) 5
Importantly, 73% of cirrhotic patients with an initial low SAAG who undergo repeat paracentesis convert to a high SAAG, suggesting measurement error or transient conditions 5. Therefore, repeat paracentesis is recommended as part of the workup when a low SAAG is found in a patient with known or suspected cirrhosis 5.
Additional Workup Required
Since low SAAG does not differentiate between specific causes, additional testing is essential:
- Cell count with differential to evaluate for spontaneous bacterial peritonitis (PMN >250 cells/mm³) 1, 4
- Culture in blood culture bottles at bedside if infection is suspected 1
- Cytology if malignancy is suspected (though sensitivity is limited) 1, 4
- Acid-fast bacilli smear, culture, and adenosine deaminase (ADA) assay if tuberculous peritonitis is suspected 1
- Total protein, glucose, and lactate dehydrogenase if secondary bacterial peritonitis is suspected 1
Management Implications
Patients with low SAAG ascites generally do not respond to sodium restriction and diuretics (except nephrotic syndrome) and require treatment of the underlying disorder 2, 4. This contrasts sharply with high SAAG ascites (≥1.1 g/dL), where sodium restriction and diuretics are the mainstay of therapy 2, 4.