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Biochemistry
SAAG isn't a test you can order on its own — it's a subtraction. A doctor drains a sample of ascitic fluid (fluid built up in the abdomen) and takes a blood sample around the same time; the lab measures albumin in both, and SAAG is the blood albumin figure minus the fluid albumin figure. That gap tells your doctor whether the fluid is being pushed out by raised pressure in the veins draining the liver — portal hypertension — or by something else, like cancer or infection in the abdominal lining. It has replaced an older method reading the fluid's own protein level, since SAAG sorts causes of ascites more reliably.
The result is reported as a single number in grams per decilitre: your blood albumin minus your ascitic fluid albumin, taken from samples drawn close together in time. A gradient of 1.1 g/dL or higher points toward portal hypertension — pressure backing up in the veins that drain into the liver, most often from cirrhosis. A gradient below 1.1 g/dL points away from portal hypertension and toward other causes, such as cancer that has spread to the abdominal lining, tuberculosis of the peritoneum, or pancreatitis.
The reasoning behind SAAG is about pressure and fluid movement, not disease itself. When pressure builds up in the portal vein system — the vessels carrying blood from the gut through the liver — fluid gets pushed out into the abdominal cavity, but albumin, being a large protein, is left behind in the blood more than water is. That gap between blood albumin and fluid albumin ends up tracking how much portal pressure is present, which is why it's a gradient rather than a single fluid measurement read on its own.
A gradient of 1.1 g/dL or above is reported to identify portal hypertension with roughly 97 percent accuracy, most commonly from cirrhosis, but also from conditions like heart failure or a blocked hepatic vein that raise pressure the same way. A gradient below 1.1 g/dL means something different is leaking the fluid out — cancer cells irritating the lining, an infection like tuberculosis, or inflammation from pancreatitis — none of which raise portal pressure the way liver scarring does.
Because SAAG depends on comparing two albumin levels taken close together, the fluid draw and the blood draw are timed near each other rather than days apart. The fluid draw itself is a short procedure called paracentesis, done by a doctor; ask your doctor or the centre what to expect beforehand.
Both, together. It's calculated from an albumin measurement in your blood and an albumin measurement in fluid drained from your abdomen, taken close to the same time — neither number on its own gives the SAAG result.
It points toward portal hypertension, raised pressure in the veins that carry blood from the gut through the liver. Cirrhosis is the most common cause, though heart failure and some vein blockages can produce the same pattern.
It points away from portal hypertension and toward other causes of abdominal fluid, such as cancer that has spread to the abdominal lining, tuberculosis of the peritoneum, or pancreatitis.
The older method, based on the fluid's own total protein level, turned out to be unreliable for ascites — especially when infection was also present. SAAG has been shown to classify the underlying cause more accurately.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Through a short procedure called paracentesis, where a doctor drains fluid from your abdomen using a needle, usually under local anaesthesia. Ask your doctor or the centre about preparation and what to expect.
No. It narrows the underlying cause into one of two broad categories — portal hypertension or not — but confirming the exact condition usually needs imaging, other fluid tests, or a clinical history alongside it.