π§ͺ SAAG Calculator
What is driving the ascites? The gradient knows.
For informational purposes only, not medical advice. Consult a healthcare professional.
The serum-ascites albumin gradient is the single best test for sorting ascites causes: subtract ascitic fluid albumin from serum albumin, and a gradient of 1.1 g/dL or more means portal hypertension with about 97 percent accuracy. It replaced the old transudate-versus-exudate classification because it performs better. High-gradient causes include cirrhosis, heart failure, and Budd-Chiari; low-gradient causes include peritoneal carcinomatosis, tuberculosis, and pancreatic ascites. This calculator computes it for clinical teaching and reference.
How to Use This Calculator
Enter serum albumin and ascitic fluid albumin in g/dL from samples drawn near the same time. The calculator subtracts and classifies the gradient.
Use albumin values from the same day: serum from blood work and ascitic fluid from the diagnostic paracentesis.
Enter both in g/dL. If the lab reports g/L, divide by 10 first.
Read the gradient. At or above 1.1 points to portal hypertension; below points away from it.
How the Math Works
SAAG equals serum albumin minus ascitic fluid albumin, both in g/dL. With serum 3.2 and ascitic 1.5, the gradient is 1.7. The 1.1 threshold comes from validation studies showing it identifies portal hypertension far more accurately than total protein criteria. The physiology: portal hypertension raises hydrostatic pressure, driving low-protein fluid across with a preserved albumin gap, while peritoneal disease leaks protein-rich fluid that narrows the gap. Diuretics can raise SAAG slightly by concentrating serum albumin, a nuance worth knowing in treated patients.
Worked Example
Serum albumin 3.2 with ascitic albumin 1.5 gives a SAAG of 1.70 g/dL, which the calculator classifies as High gradient: portal hypertension. In a patient with known liver disease this confirms the ascites is portal-hypertensive, and management follows the cirrhosis pathway: sodium restriction, diuretics, and variceal screening. The same fluid with serum albumin 2.0 would give 0.5 and send the workup toward peritoneal causes instead.
Reading Your Result
High gradient at 1.1 or above means portal hypertension is driving the fluid: cirrhosis most often, then cardiac causes and portal vein thrombosis. Low gradient under 1.1 means look at the peritoneum itself: malignancy, infection including TB, pancreatic or biliary leaks. Either way, ascitic fluid cell count, culture, and total protein complete the picture, and a neutrophil count at or above 250 defines spontaneous bacterial peritonitis regardless of gradient.
| SAAG | Meaning | Usual causes |
|---|---|---|
| 1.1+ | Portal hypertension | Cirrhosis, heart failure, Budd-Chiari |
| Under 1.1 | Non-portal | Carcinomatosis, TB, pancreatic |
Limitations
SAAG needs near-simultaneous samples; albumin shifts with infusions and diuresis. It identifies the physiology, not the specific disease: cirrhosis versus cardiac still needs the clinical picture. Mixed causes exist, and the gradient performs less cleanly in them. Paracentesis interpretation belongs with the treating team, not a calculator alone.
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For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is SAAG?
Serum-ascites albumin gradient: serum albumin minus ascitic fluid albumin. At 1.1 g/dL or above it indicates portal hypertension with about 97%% accuracy. The standard first test for classifying new ascites.
Why is 1.1 the cutoff?
It emerged from validation studies as the threshold best separating portal-hypertensive from non-portal ascites, outperforming the older transudate-exudate protein criteria. It has held up across decades of use.
What causes high SAAG ascites?
Portal hypertension: cirrhosis most commonly, plus right heart failure, constrictive pericarditis, Budd-Chiari syndrome, and portal vein thrombosis. The gradient says the mechanism; the history and exam name the disease.
What causes low SAAG ascites?
Peritoneal disease: carcinomatosis, tuberculous peritonitis, pancreatic ascites, biliary leak, and nephrotic syndrome. These leak protein-rich fluid that narrows the albumin gap. Malignancy workup and infection testing follow.
How is ascitic fluid obtained?
By paracentesis: a needle into the peritoneal cavity, usually under ultrasound guidance, done diagnostically for every new ascites. It is a bedside procedure with low complication rates in experienced hands.
What is spontaneous bacterial peritonitis?
Infection of ascitic fluid without a surgical source, diagnosed by neutrophils at or above 250 per microliter in the fluid. It complicates cirrhotic ascites and needs prompt antibiotics. The cell count matters regardless of SAAG.
Do diuretics affect SAAG?
They can raise it modestly by hemoconcentration, increasing serum albumin more than ascitic albumin. The effect is small relative to the 1.1 threshold but worth knowing when interpreting borderline gradients in treated patients.
What is the old transudate-exudate system?
Classifying ascitic fluid by total protein above or below 2.5 g/dL. SAAG replaced it because protein misclassifies cardiac ascites and diuretic-treated cirrhosis. Some still quote protein alongside SAAG for additional context.
Can SAAG be high in heart failure?
Yes. Cardiac ascites is portal-hypertensive physiology from venous congestion, so the gradient runs high, typically with high protein too. The exam and echo separate it from cirrhosis.
Does SAAG diagnose cirrhosis?
No. It identifies portal hypertension as the mechanism, which cirrhosis commonly causes. Imaging, labs, and sometimes biopsy establish the liver diagnosis. The gradient is the sorting step, not the final answer.