Low AST (SGOT) blood test: what a low aspartate aminotransferase means

A low AST usually means very little of the enzyme is leaking from damaged cells, or that the enzyme is present but measured low because your sample is short of vitamin B6. Aspartate aminotransferase (AST, called SGOT on older reports) works inside liver, muscle, heart, kidney and red blood cells, and a blood test picks up only the share that escapes. A low result is not a grade on how well your liver works.

What counts as a low AST?

Adult AST reference ranges on US reports often run from about 8 to 33 U/L (units per liter, a measure of enzyme activity), though some labs print 10 to 40 U/L, and the ACG guideline on abnormal liver tests notes that cutoffs differ between laboratories ¹. Some reports show only an upper limit, written as something like "under 40", which means that lab does not flag a low AST at all. Where a lab does print a lower limit, it usually marks the bottom of the middle 95% of a healthy reference group, so a few healthy people in every hundred land below it by design. Our page on how reference ranges are built explains why that matters.

Usually, you will have low levels of AST in your blood.MedlinePlus, AST blood test (US National Library of Medicine)

MedlinePlus means that the normal state is a small amount of AST in blood, because healthy cells keep the enzyme inside them ². A low AST sits at the quiet end of that normal state.

Why AST can read low

Labs measure AST by how much chemical work the enzyme does in your sample. AST can only do that work with pyridoxal-5'-phosphate (P5P, the active form of vitamin B6) attached to it.

The most careful lab method adds extra P5P to the test so a B6 shortage cannot skew it. Many everyday methods do not. So if you are short of B6, you can have plenty of AST in your blood and still get a low result ⁵.

What causes low AST levels

Most of these causes sit outside the liver. Roughly in order of how often they explain a low AST:

• Normal variation. Lean, healthy people with little cell turnover often sit at the bottom of the AST range, and some fall below a printed lower limit.
• Low vitamin B6. More common in older adults, people who drink heavily, people on dialysis, and people taking isoniazid or some anti-seizure drugs. Low B6 can also cause cracked corners of the mouth, a sore tongue, low mood or confusion ⁶.
• Chronic kidney disease and dialysis. People on hemodialysis have lower AST and ALT than the general population, likely from B6 loss and toxins that hold back the enzymes ³.
• Low muscle mass, frailty and older age. Muscle holds aminotransferases, and low ALT in older adults tracks sarcopenia (age-related muscle loss) ⁴; AST may behave in a similar way, though it has been studied less.
• Malnutrition or very low protein intake, which lowers enzyme production and B6 together.
• A drug or lab effect. The antibiotic metronidazole can make AST and ALT read falsely low on some lab methods; a repeat on another day, or at another lab, settles it.

If kidney disease is on your list, read what chronic kidney disease means at each stage, see how to read your kidney panel, and check your filtration number below.

CalculatoreGFR calculatorA low AST plus a low eGFR points toward a kidney cause.Work it out

Low AST and low ALT together

When AST and ALT are both low, the same short list applies: low vitamin B6, dialysis, or low muscle mass. Vitamin B6 lack suppresses ALT more than AST. In a study of alcoholic hepatitis, Diehl and colleagues linked P5P deficiency to the very high AST/ALT ratio seen in that illness, because ALT activity fell further ⁵. So in someone short of B6, the AST/ALT ratio can rise for reasons other than liver scarring, so the ratio alone should not be read as a scarring signal.

In older adults, low enzymes carry a separate meaning. A study by Vespasiani-Gentilucci and colleagues found that low ALT in elderly people tracks frailty, sarcopenia, disability and shorter survival ⁴. The low enzyme causes no harm itself; it reflects less muscle and less physical reserve. For an older person with a low AST and low ALT, the useful conversation is about strength, weight and nutrition.

Does a low AST mean my liver is healthy?

No. AST measures injury (enzyme leaking from damaged cells), and the ACG guideline is clear that AST and ALT are markers of liver cell injury, not tests of liver function ¹. A liver can be fatty, or even scarred, while AST sits in the normal or low range, which is why fatty liver is often missed when people rely on enzymes alone ⁸. If you have risk factors such as type 2 diabetes, a large waist or heavy drinking, a low AST does not clear you.

Our guide to reading a liver panel line by line covers each of these markers, and clotting tests explained covers INR. If your albumin is low as well, read what a low albumin means: next to a low AST it points to poor nutrition or illness.

When a low AST is worth a closer look

A low AST with an otherwise normal panel, in someone who feels well, usually needs no action. Raise the result with your clinician if the low AST comes with any of the items below.

• A low albumin, unplanned weight loss or visible muscle loss
• Cracked corners of the mouth, a sore tongue, new confusion, or numbness or tingling in the hands or feet (possible B6 deficiency)
• Chronic kidney disease or dialysis
• Heavy drinking
• A sharp fall from your usual AST with no clear reason

What to do next

1. 1Repeat it at the same labDifferent methods give different AST values, and a single reading can be noise. AST clears from blood in about 17 hours ⁷, so a repeat in 2 to 4 weeks, or at your next routine test, is enough. Our guide on why a trend beats a single reading explains how to compare results.
2. 2Read the whole panelLook at ALT, creatinine and eGFR, albumin and bilirubin together; our guide to reading a CMP line by line walks through each. A low AST with normal neighbors is almost always fine.
3. 3Ask about vitamin B6 if you have a risk factorOlder age, heavy drinking, dialysis, poor appetite, isoniazid or anti-seizure drugs, or the symptoms above are reasons to ask for a plasma P5P test.
4. 4Treat the causeThere is no benefit in raising AST itself. If B6 is low, B6-rich foods such as chickpeas, fish, poultry, potatoes and bananas help, and your clinician can say whether a B complex fits.

For everything else about this enzyme, including what raises it, start at the AST marker page, and browse the liver topic for the full set of liver markers. For liver support more broadly, see supplements for liver health.

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