SAAG: how the serum-ascites albumin gradient is calculated

The serum-ascites albumin gradient (SAAG) is serum albumin minus ascites albumin, both in g/dL, from paired serum and ascitic fluid samples. Magent's calculator rounds the result to one decimal and flags it when it's 1.1 or more. Serum albumin 3.5 and ascites albumin 2.0 give a SAAG of 1.5.

Not a medical device. Not a diagnosis or dosing recommendation.

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Liver calculators
Runyon BA et al. · 1992
The SAAG formula
Worked examples
Frequently asked questions

What is the SAAG?

The SAAG compares albumin in the blood with albumin in ascitic fluid. Magent's calculator cites Bruce A. Runyon and colleagues, published in Annals of Internal Medicine in 1992. Their abstract describes collecting paired serum and ascitic fluid samples from consecutive patients with all forms of ascites, and comparing the albumin gradient with the older exudate-transudate approach based on the fluid's total protein.

The calculator returns the gradient and a true/false field, portal_hypertension_physiology, which is true when the rounded gradient is >= 1.1 g/dL. A gradient of exactly 1.1 counts; 1.0 doesn't.

This page explains the arithmetic, the rounding and the >= 1.1 comparison. It doesn't say what a result means for a particular person.

The SAAG formula

SAAG (g/dL) = serum albumin (g/dL) − ascites albumin (g/dL)
rounded to 1 decimal
portal_hypertension_physiology = SAAG >= 1.1

Exact expression the calculator uses:

saag_g_dl = albumin_g_dl - ascites_albumin_g_dl

Inputs

Input	Meaning	Accepted range
`albumin_g_dl`	Serum albumin, g/dL	1 to 6
`albumin_g_l`	Serum albumin, g/L (instead of g/dL)	10 to 60
`ascites_albumin_g_dl`	Ascites albumin, g/dL	0.1 to 6
`ascites_albumin_g_l`	Ascites albumin, g/L (instead of g/dL)	1 to 60

How the calculation works

Get both albumins in g/dL. A value in g/L is divided by 10, so 35 g/L becomes 3.5 g/dL.
Subtract ascites albumin from serum albumin.
Round the result to one decimal.
Compare the rounded value with 1.1. At 1.1 or above, portal_hypertension_physiology is true.

Units

Give each albumin once, in g/dL or in g/L, not both. You can mix units: serum in g/dL with ascites in g/L works. A missing value, a value given in both units, or one outside the range is rejected with an error. The calculator returns both albumins in g/dL, the gradient and the true/false field.

Worked examples

These use Magent's own expected values for the calculator.

Example 1: serum 3.5 g/dL, ascites 2.0 g/dL

SAAG = 3.5 − 2.0 = 1.5 g/dL.
1.5 is 1.1 or more → portal_hypertension_physiology true.

Example 2: serum 35 g/L, ascites 20 g/L

Serum 35 ÷ 10 = 3.5 g/dL; ascites 20 ÷ 10 = 2.0 g/dL.
SAAG = 3.5 − 2.0 = 1.5 g/dL → true.

Example 3: exactly at the cutoff, serum 3.0 g/dL, ascites 1.9 g/dL

SAAG = 3.0 − 1.9 = 1.1 g/dL after rounding.
1.1 is 1.1 or more → portal_hypertension_physiology true.

Example 4: just below, serum 3.0 g/dL, ascites 2.0 g/dL

SAAG = 3.0 − 2.0 = 1.0 g/dL.
1.0 is below 1.1 → portal_hypertension_physiology false.

Example 5: mixed units, serum 3.5 g/dL, ascites 20 g/L

Ascites 20 ÷ 10 = 2.0 g/dL.
SAAG = 3.5 − 2.0 = 1.5 g/dL → true.

History of the SAAG

The calculator cites Runyon BA, Montano AA, Akriviadis EA, Antillon MR, Irving MA and McHutchison JG, Annals of Internal Medicine, 1992 (volume 117, issue 3, pages 215–220). The abstract compares the albumin gradient with the exudate-transudate concept for classifying ascites.

When it's used

The 1992 study used paired serum and ascitic fluid samples, so the gradient needs an albumin result from each.

Where it's used

The 1992 study was set on the hepatology ward and consult service of a large urban hospital. The calculator needs two lab results: serum albumin and ascitic fluid albumin.

Who uses it

The person using the calculator enters the two albumin results. The calculator converts units, subtracts, rounds and compares with 1.1.

Limits of the calculation

It's a gradient. It doesn't confirm or rule out portal hypertension or peritonitis.
It isn't an exudate/transudate rule for ascites.
The comparison uses the rounded value, so 1.1 counts and 1.0 doesn't.
This page doesn't say what to do with a result.

Clinical decisions belong to a qualified clinician who knows the patient.

Child-Pugh score is a separate cirrhosis score built from bilirubin, albumin, INR, encephalopathy and ascites. It doesn't use ascitic fluid albumin.
Light's criteria is a separate exudate/transudate rule for pleural fluid, not ascites.

Glossary

Ascites: fluid collecting in the abdomen.
Albumin: the main protein in blood plasma.
Gradient: here, the difference between serum and ascites albumin.
Portal hypertension: raised pressure in the vein system that drains the gut into the liver.

Common mistakes

Subtracting the wrong way. It's serum minus ascites.
Mixing g/L and g/dL without converting. Give each value with its unit field; the calculator divides g/L by 10.
Treating 1.1 as below the cutoff. The calculator uses >= 1.1, so 1.1 counts.
Entering one albumin in both units. Each value goes in once.

Source

Runyon BA, Montano AA, Akriviadis EA, Antillon MR, Irving MA, McHutchison JG. Ann Intern Med. 1992;117(3):215-220. DOI: 10.7326/0003-4819-117-3-215. PMID: 1616215

Frequently asked questions

How do you calculate the SAAG?

Subtract ascites albumin from serum albumin, both in g/dL. Serum 3.5 and ascites 2.0 give 1.5.

Is a SAAG of exactly 1.1 counted?

Yes. The calculator uses >= 1.1, so a rounded SAAG of 1.1 sets portal_hypertension_physiology to true. A SAAG of 1.0 doesn't.

Can I enter albumin in g/L?

Yes. The calculator divides g/L by 10 to get g/dL. You can give serum and ascites albumin in different units.

Does the SAAG use total protein?

No. It uses albumin alone.