Serum-Ascites Albumin Gradient (SAAG)

Q: What is SAAG and how is it calculated?

SAAG (Serum-Ascites Albumin Gradient) is the difference between serum albumin and ascitic fluid albumin, both measured in g/dL. It is calculated as: SAAG = Serum albumin − Ascites albumin.

Q: What does a SAAG ≥1.1 g/dL mean?

A SAAG ≥1.1 g/dL indicates that portal hypertension is the cause of ascites. Common causes include liver cirrhosis, congestive heart failure, and Budd-Chiari syndrome. The gradient is maintained because the elevated hydrostatic pressure in the portal system forces albumin-rich fluid into the peritoneal cavity.

Q: What does a SAAG <1.1 g/dL mean?

A SAAG <1.1 g/dL indicates non-portal hypertensive causes of ascites, such as peritoneal carcinomatosis, tuberculosis, nephrotic syndrome, or pancreatic ascites. These conditions cause ascites through mechanisms other than elevated portal pressure.

Q: When should SAAG not be used?

SAAG may be unreliable in mixed ascites (e.g., cirrhosis with concurrent cancer), severe hypoalbuminemia (serum albumin <2.8 g/dL), or when serum and ascitic fluid samples are not collected simultaneously.

Q: How does SAAG compare to the transudate/exudate classification?

SAAG is superior to the traditional transudate/exudate classification (based on ascitic fluid protein) for classifying ascites. SAAG correctly classifies >90% of ascites, while the protein-based method misclassifies up to 20-30% of cases due to the confounding effect of serum albumin.

Calculates the gradient between serum albumin and ascitic fluid albumin to classify ascites as portal hypertensive (SAAG ≥1.1 g/dL) or non-portal hypertensive (SAAG <1.1 g/dL). First-line diagnostic tool for ascites workup.

Gastroenterology Internal MedicineEvidence-BasedUpdated 2026-08

Clinical Notes

Formula

SAAG = Serum albumin (g/dL) − Ascites albumin (g/dL)

Normal Range

≥1.1 g/dL (portal hypertension)

Clinical Notes

The SAAG was introduced by Boyer et al. in 1968 and is the single most reliable test for classifying ascites. A SAAG ≥1.1 g/dL correctly identifies portal hypertension with >90% accuracy. It replaces the older transudate/exudate classification, which was unreliable for ascites due to the confounding effect of serum albumin on ascitic fluid protein.

Calculator Information

Specialty

Internal Medicine

📋 Reference Ranges

Normal Range

≥1.1 g/dL (portal hypertension)

Reference ranges for this calculator
Classification	Range
Portal hypertension	≥1.1 g/dL
Non-portal hypertension	<1.1 g/dL

What This Calculator Measures

Calculates the Serum-Ascites Albumin Gradient (SAAG) to classify ascites as portal hypertensive (SAAG ≥1.1 g/dL) or non-portal hypertensive (SAAG <1.1 g/dL). This is the first-line diagnostic tool for ascites workup.

How to Use

Obtain serum albumin and ascitic fluid albumin from the same blood draw.
Enter both values in g/dL (multiply g/L by 0.1 to convert).
The calculator computes the gradient and classifies the ascites.
SAAG ≥1.1 g/dL indicates portal hypertension as the cause of ascites.
SAAG <1.1 g/dL indicates non-portal hypertensive causes.

Interpretation Guide

SAAG ≥1.1 g/dL is consistent with portal hypertension (cirrhosis, heart failure, Budd-Chiari). SAAG <1.1 g/dL suggests peritoneal carcinomatosis, tuberculosis, nephrotic syndrome, or pancreatic ascites. The gradient must be interpreted alongside ascitic fluid cell count, protein, glucose, and cytology.

Clinical Significance

SAAG is the single most reliable test for classifying ascites, replacing the older transudate/exudate classification. It correctly identifies portal hypertension with >90% accuracy and guides the subsequent diagnostic workup.

When to Use

Any patient with new-onset or unexplained ascites
Initial workup to classify ascites etiology
When the cause of ascites is uncertain
Before deciding on further diagnostic testing (e.g., diagnostic paracentesis)

When Not to Use

When the cause of ascites is clinically obvious (e.g., known decompensated cirrhosis with typical features)
In mixed ascites (cirrhosis with concurrent peritoneal carcinomatosis)
When serum albumin is <2.8 g/dL (may reduce accuracy)

Limitations

SAAG must be measured simultaneously from serum and ascitic fluid.
Hypoalbuminemia (<2.8 g/dL) may reduce SAAG accuracy.
SAAG is unreliable in mixed ascites.
Does not identify the specific cause of portal hypertension or non-portal hypertensive ascites.

Worked Example

A patient with known cirrhosis presents with new-onset ascites. Serum albumin is 3.2 g/dL and ascitic fluid albumin is 1.0 g/dL.

Inputs:

serum-albumin: 3.2

ascites-albumin: 1.0

SAAG = 3.2 − 1.0 = 2.2 g/dL (≥1.1 g/dL). Consistent with portal hypertension from cirrhosis.

Evidence

Source: Gastroenterology
Reference: Boyer TD, et al. Arch Intern Med. 1968;122(5):425-428.
Reviewed By: MedCalcHub Clinical Team
Version: 1.0
Updated: 2026-08

Boyer TD, et al. Arch Intern Med. 1968;122(5):425-428.
Runyon BA, et al. N Engl J Med. 1983;309(22):1340-1344.

References

Boyer TD, Kahn AM, Reynolds TB. Arch Intern Med. 1968;122(5):425-428. (Diagnostic study)
Runyon BA, Hoefs JC, Morgenthaler US. N Engl J Med. 1983;309(22):1340-1344. (Validation study)

Frequently Asked Questions

What is SAAG and how is it calculated?

SAAG (Serum-Ascites Albumin Gradient) is the difference between serum albumin and ascitic fluid albumin, both measured in g/dL. It is calculated as: SAAG = Serum albumin − Ascites albumin.

What does a SAAG ≥1.1 g/dL mean?

A SAAG ≥1.1 g/dL indicates that portal hypertension is the cause of ascites. Common causes include liver cirrhosis, congestive heart failure, and Budd-Chiari syndrome. The gradient is maintained because the elevated hydrostatic pressure in the portal system forces albumin-rich fluid into the peritoneal cavity.

What does a SAAG <1.1 g/dL mean?

A SAAG <1.1 g/dL indicates non-portal hypertensive causes of ascites, such as peritoneal carcinomatosis, tuberculosis, nephrotic syndrome, or pancreatic ascites. These conditions cause ascites through mechanisms other than elevated portal pressure.

When should SAAG not be used?

SAAG may be unreliable in mixed ascites (e.g., cirrhosis with concurrent cancer), severe hypoalbuminemia (serum albumin <2.8 g/dL), or when serum and ascitic fluid samples are not collected simultaneously.

How does SAAG compare to the transudate/exudate classification?

SAAG is superior to the traditional transudate/exudate classification (based on ascitic fluid protein) for classifying ascites. SAAG correctly classifies >90% of ascites, while the protein-based method misclassifies up to 20-30% of cases due to the confounding effect of serum albumin.

Disclaimer: This calculator is intended for educational and clinical decision support. SAAG should be interpreted with ascitic fluid analysis and clinical context. It does not replace comprehensive clinical assessment.