Serum–Ascites Albumin Gradient (SAAG): Sorting Portal from Non-Portal Ascites

What it is

The Serum–Ascites Albumin Gradient (SAAG) classifies ascites by the mechanism producing it, rather than by the older exudate/transudate protein dichotomy. It rests on a physiological fact: in portal hypertension, the high hydrostatic pressure forces a relatively albumin-poor ultrafiltrate into the peritoneum, so the gap between serum and ascitic albumin is wide. When ascites arises from other processes (peritoneal disease, malignancy), albumin leaks more freely and the gap is narrow.

The formula

SAAG (g/dL) = serum albumin − ascitic fluid albumin

Both albumins must be from samples drawn the same day (ideally close together), because serum albumin shifts with the patient’s clinical state.

Interpreting the gradient

• SAAG ≥ 1.1 g/dL — portal hypertension is likely, with roughly 97% accuracy. Causes include cirrhosis, alcoholic hepatitis, heart failure, Budd–Chiari syndrome, massive hepatic metastases.
• SAAG < 1.1 g/dL — a non-portal cause is more likely: tuberculous peritonitis, peritoneal carcinomatosis / malignancy, nephrotic syndrome, pancreatic ascites, serositis.

The cut-off is a clean binary at 1.1 g/dL (equivalently 11 g/L). The gradient tells you the mechanism, not the specific disease — it narrows the differential, it does not close it.

When to use it

Calculate SAAG on every new diagnostic paracentesis as the first step in working up ascites. It is the single most useful classifier and outperforms the transudate/exudate framework. Pair it with ascitic total protein (helps separate cardiac ascites, often high-SAAG but high-protein, from cirrhotic ascites) and a cell count (to screen for spontaneous bacterial peritonitis).

Worked example

A child with suspected cirrhosis: serum albumin 3.5 g/dL, ascitic albumin 0.8 g/dL. SAAG = 3.5 − 0.8 = 2.7 g/dL → ≥1.1, portal hypertension likely — consistent with cirrhosis.

Contrast: serum albumin 3.0 g/dL, ascitic albumin 2.4 g/dL. SAAG = 0.6 g/dL → <1.1, pointing to a non-portal cause such as TB peritonitis or malignancy, which should redirect the work-up (adenosine deaminase, cytology, imaging).

Pitfalls and caveats

• Same-day samples are mandatory. A serum albumin from a different day invalidates the gradient.
• Two processes can coexist — e.g. cirrhosis plus peritoneal TB. A high SAAG does not exclude a second pathology; correlate clinically.
• High-SAAG is not synonymous with cirrhosis — heart failure and Budd–Chiari also produce a high gradient. Use ascitic protein and the clinical picture to discriminate.
• Severe hypoalbuminaemia or lipid/measurement artefacts can blur a borderline result; repeat or corroborate when the value sits near 1.1.

Run it: Serum–Ascites Albumin Gradient (SAAG)

Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.