🧫 SAAG Calculator
Determine whether ascites is due to portal hypertension by subtracting ascitic fluid albumin from serum albumin.
SAAG = Serum albumin − Ascitic albumin (same units, typically g/dL).
How to Use This Calculator
Obtain paired albumin samples
Measure serum albumin and ascitic fluid albumin from samples collected at the same time to avoid misclassification due to temporal changes.
Enter values in matching units
Typically both are reported in g/dL. If reported in g/L, convert by dividing by 10 before entering.
Interpret with clinical context
Use SAAG to differentiate portal hypertensive from non-portal causes, then correlate with imaging, history, and other ascitic fluid tests (cell count, protein, LDH).
Formula
Serum-Ascites Albumin Gradient (SAAG) is calculated as:
- SAAG = Serum albumin − Ascitic fluid albumin (expressed in g/dL)
- High SAAG (≥1.1 g/dL) indicates portal hypertension in ~97% of cases
- Low SAAG (<1.1 g/dL) indicates non-portal causes of ascites
The gradient reflects the oncotic pressure difference caused by portal hypertension, where portal pressures drive fluid with low albumin content into the peritoneal cavity.
Full Description
SAAG has largely replaced total protein concentration for ascites classification. It reliably distinguishes portal hypertensive causes (cirrhosis, cardiac failure) from peritoneal causes (malignancy, infection). High SAAG ascites should prompt evaluation for cirrhosis complications or cardiac/hepatic venous outflow obstruction.
Combine SAAG with total protein, cytology, cell count, cultures, and imaging. For example, high SAAG + high protein suggests cardiac ascites, while high SAAG + low protein suggests cirrhotic ascites. Always consider bacterial peritonitis in patients with cirrhosis and fever or abdominal pain irrespective of SAAG.
Persistent or unexplained ascites may require diagnostic laparoscopy, biopsy, or advanced imaging to characterise the underlying pathology.
Frequently Asked Questions
Can SAAG be used in patients on diuretics?
Yes. SAAG remains accurate even when diuretics alter total protein levels, making it superior to the old transudate/exudate classification.
What if serum albumin is very low?
Low serum albumin (e.g., severe malnutrition) can yield low SAAG despite portal hypertension. Interpret with caution and consider overall context.
Should I calculate SAAG for every paracentesis?
It is most useful during diagnostic paracentesis to establish etiology. Repeat calculations may help if the clinical picture changes or new causes are suspected.
Does SAAG predict spontaneous bacterial peritonitis?
No. SBP risk correlates with total protein (<1 g/dL) and neutrophil count, not the gradient. Always send fluid for cell count and culture.
How do I convert g/L to g/dL?
Divide g/L by 10 to obtain g/dL. Ensure both serum and ascitic values use the same unit before calculating SAAG.