How do I calculate the serum‑ascites albumin gradient (SAAG)?

How to Calculate SAAG

The serum-ascites albumin gradient (SAAG) is calculated by subtracting the ascitic fluid albumin concentration from the simultaneously obtained serum albumin concentration. 1

Calculation Formula

SAAG = Serum Albumin − Ascitic Fluid Albumin

Both values must be measured in the same units (g/dL) and obtained at the same time to ensure accuracy. 1, 2

Interpretation Thresholds

• SAAG ≥ 1.1 g/dL indicates portal hypertension with approximately 97% diagnostic accuracy, most commonly from cirrhosis (>85% of cases), but also cardiac ascites, Budd-Chiari syndrome, or massive hepatic metastases. 1

• SAAG < 1.1 g/dL excludes portal hypertension and points toward peritoneal carcinomatosis, tuberculous peritonitis, pancreatic disease, or nephrotic syndrome. 1

Clinical Pearls for Accurate Calculation

• Timing is critical: Draw serum and ascitic fluid samples simultaneously or within the same clinical encounter to avoid fluctuations in serum albumin that could skew the gradient. 1

• Negative SAAG values: Rarely, you may encounter a negative SAAG (ascitic albumin exceeds serum albumin), which has been reported in unusual malignancies like cholangiocarcinoma; this still represents a low gradient (<1.1 g/dL) and suggests non-portal causes. 3

• SAAG replaces outdated exudate-transudate classification: The older protein-based system misclassifies cardiac ascites as an exudate; SAAG correctly identifies it as portal-hypertension-related (≥1.1 g/dL) while the high total protein (>2.5 g/dL) distinguishes cardiac from cirrhotic etiology. 1, 2

When to Calculate SAAG

• Mandatory for all new-onset ascites in both inpatient and outpatient settings as part of the initial diagnostic workup. 1

• Not required for recurrent ascites once the underlying cause is established, though cell count remains mandatory to screen for spontaneous bacterial peritonitis. 1