SAAG Calculator
Enter the albumin concentration from a serum sample and a same-day ascitic fluid sample to get the SAAG value. A result above 1.1 g/dL indicates portal hypertension with about 97% accuracy; below 1.1 g/dL suggests peritoneal or non-portal causes. The results panel shows the computed gradient, its clinical category, a colour-coded gauge, a worked-out calculation, and a detailed interpretation with next steps.
Formula
Worked example
A patient has a serum albumin of 3.5 g/dL and an ascitic fluid albumin of 1.8 g/dL, both drawn the same morning. SAAG = 3.5 - 1.8 = 1.7 g/dL, which is above the 1.1 g/dL threshold, consistent with portal hypertension.
What is the SAAG and why does it matter?
The serum-ascites albumin gradient (SAAG) is calculated by subtracting the albumin concentration in ascitic fluid from the albumin concentration in blood serum, both measured on the same day. It quantifies oncotic pressure differences between the two compartments and reliably identifies whether elevated portal pressure is driving fluid accumulation in the abdomen. When the gradient is 1.1 g/dL or higher, portal hypertension is present with approximately 97% accuracy, making SAAG one of the most clinically useful single-value tests in hepatology and gastroenterology. The SAAG replaced the older transudate/exudate classification, which relied on total protein alone and had substantially lower accuracy.
How to obtain accurate samples
Accuracy depends on both albumin measurements being taken as close together in time as possible, ideally on the same day from the same patient encounter. Serum albumin is obtained from a routine venous blood draw. Ascitic albumin is obtained via diagnostic paracentesis, where a needle is used to withdraw a small volume of peritoneal fluid from the abdomen. Because albumin concentrations in serum fluctuate with hydration, nutrition and illness, any significant gap between the two draws can reduce the reliability of the gradient. Most published studies and clinical guidelines specify same-day sampling as a minimum requirement.
High SAAG: portal hypertension and its causes
A SAAG at or above 1.1 g/dL indicates that hydrostatic pressure in the portal venous system is forcing fluid through the capillary walls into the peritoneal space. Cirrhosis is by far the most common cause worldwide, accounting for roughly 80% of all cases of ascites. Other portal hypertensive causes include alcoholic hepatitis, hepatic vein occlusion (Budd-Chiari syndrome), portal vein thrombosis, congestive heart failure (cardiac ascites), and inferior vena cava obstruction. Ascitic fluid total protein (AFTP) helps distinguish these: cirrhosis typically produces AFTP below 2.5 g/dL, while cardiac and Budd-Chiari ascites often shows AFTP above 2.5 g/dL because the sinusoidal origin produces a richer protein leak.
Low SAAG: non-portal and peritoneal causes
A SAAG below 1.1 g/dL means the oncotic gradient between serum and ascites is small, pointing away from portal hypertension toward direct peritoneal disease or systemic protein loss. The most important causes are peritoneal carcinomatosis (malignant cells spread across the peritoneum, commonly from ovarian, colorectal, gastric or pancreatic cancer), tuberculous peritonitis (a major cause in high-prevalence regions), nephrotic syndrome (severe hypoalbuminaemia raises oncotic pressure on both sides equally), and pancreatic ascites from a duct leak. Chylous ascites from lymphatic obstruction also produces a low SAAG and is identified by markedly elevated triglycerides in the ascitic fluid. Peritoneal fluid cytology, culture, amylase, LDH, and triglycerides are the next steps when SAAG is below the threshold.
SAAG interpretation and common causes
| SAAG | Threshold | Likely mechanism | Common causes |
|---|---|---|---|
| High | >= 1.1 g/dL (>= 11 g/L) | Portal hypertension | Cirrhosis, alcoholic hepatitis, cardiac ascites, portal vein thrombosis, Budd-Chiari syndrome, hepatic failure |
| Low | < 1.1 g/dL (< 11 g/L) | Non-portal / peritoneal | Tuberculous peritonitis, peritoneal carcinomatosis, nephrotic syndrome, pancreatitis, biliary ascites, chylous ascites |
Both columns of causes are not exhaustive; clinical context and additional lab tests guide the final diagnosis.
Frequently asked questions
What does a SAAG of 1.1 g/dL mean?
The cut-off of 1.1 g/dL (equivalent to 11 g/L) is the threshold above which portal hypertension has been found to be present with roughly 97% accuracy across multiple studies. A value at exactly 1.1 is interpreted as high SAAG and is consistent with portal hypertension, though clinical context and additional tests always guide final management.
Why do both samples need to be taken on the same day?
Albumin levels in serum fluctuate with hydration, nutritional intake and the clinical course of illness. If the serum and ascitic fluid samples are drawn at different times, those fluctuations are reflected in the serum value but not in the peritoneal fluid, which has slower turnover. The resulting gradient may be artificially elevated or reduced, leading to misclassification. Guidelines from the American Association for the Study of Liver Diseases specify simultaneous or same-day sampling.
Can SAAG tell me which specific disease is causing portal hypertension?
No. SAAG identifies that portal hypertension is the mechanism, but it cannot distinguish between cirrhosis, cardiac ascites, Budd-Chiari syndrome, or other portal hypertensive states. Ascitic fluid total protein, liver function tests, imaging with Doppler ultrasound, and echocardiography are needed to identify the underlying cause.
Is SAAG accurate in patients with very low serum albumin (hypoalbuminaemia)?
SAAG retains its diagnostic validity even when serum albumin is very low. The cut-off of 1.1 g/dL was derived and validated in populations that included patients with cirrhosis-related hypoalbuminaemia. However, the absolute values will be smaller in severely hypoalbuminaemic patients, so the gradient may fall near the cut-off and should be interpreted with caution alongside clinical findings.
What units should I use for the SAAG calculator?
North American and many international labs report albumin in g/dL. Many European and UK labs report in g/L. This calculator accepts either unit - select your lab convention in the units selector and enter the values exactly as reported. Internally, the calculator converts g/L to g/dL before applying the formula (1 g/dL = 10 g/L), so the cut-off of 1.1 g/dL corresponds to 11 g/L.
Sources
- Runyon BA, et al. The serum-ascites albumin gradient is superior to the exudate-transudate concept in the differential diagnosis of ascites. Ann Intern Med. 1992.
- American Association for the Study of Liver Diseases. AASLD Practice Guidance on the Management of Ascites, Spontaneous Bacterial Peritonitis, and Hepatorenal Syndrome in Cirrhosis.