SAAG Calculator (Serum-Ascites Albumin Gradient)

How it works

SAAG = serum albumin − ascitic fluid albumin (same day, same unit) · ≥ 1.1 g/dL (11 g/L) = portal hypertension · with ascitic total protein: < 2.5 g/dL suggests cirrhosis, ≥ 2.5 g/dL heart failure or Budd-Chiari (high SAAG) or carcinomatosis/TB (low SAAG)

In portal hypertension, high pressure in the liver sinusoids pushes low-protein fluid into the abdomen, so albumin stays behind in the blood and the difference between serum and ascitic albumin is large. Runyon et al. (Ann Intern Med 1992) showed that a gradient of 1.1 g/dL or more identifies portal hypertension with about 97% accuracy, far better than the old exudate/transudate classification. Adding the ascitic total protein separates cirrhosis (low protein) from cardiac ascites and Budd-Chiari syndrome (high protein, because the sinusoids are healthy). The AASLD recommends SAAG and total protein on every diagnostic paracentesis.

Worked example

Serum albumin 30 g/L and ascitic albumin 10 g/L: SAAG = 30 − 10 = 20 g/L (2.0 g/dL), a high gradient indicating portal hypertension. With ascitic total protein of 15 g/L (1.5 g/dL, below 2.5), the pattern fits cirrhosis.

Sources: Runyon BA et al. The serum-ascites albumin gradient is superior to the exudate-transudate concept in the differential diagnosis of ascites. Ann Intern Med 1992;117:215–20 · Biggins SW et al. Diagnosis, evaluation and management of ascites, SBP and hepatorenal syndrome: 2021 AASLD practice guidance. Hepatology 2021;74:1014–48

Frequently asked questions