ALT blood test (SGPT): what high or low ALT means

What ALT measures

ALT is an enzyme, a protein that speeds up chemical reactions. Most of it sits inside liver cells, which is why ALT is more liver-specific than AST. It is reported in units per liter (U/L) and usually comes as part of a comprehensive metabolic panel (CMP) or a liver panel.

You may see it labeled ALT, SGPT (serum glutamic-pyruvic transaminase) or GPT. They are the same test.

ALT is almost always read next to AST, a related enzyme that also comes from muscle, heart and other tissues. Looking at both together tells a clinician more than either one alone.

What a high ALT can mean

Common causes of a raised ALT:

• Fatty liver. Fat building up in the liver, often alongside extra weight around the waist, high blood sugar or high triglycerides, is the most common cause of a mildly high ALT.
• Alcohol. Heavy drinking can irritate liver cells and raise ALT and AST.
• Medications and supplements. Acetaminophen can raise ALT even at usual doses. Statins occasionally do. Other prescription drugs, herbal products and dietary supplements can too.
• Hepatitis. Viral hepatitis B and C are also common causes and are checked with simple blood tests.
• Muscle injury and intense exercise. A hard workout, especially heavy lifting or a long race, can raise ALT and AST for a while afterward.
• Less common: iron overload (hemochromatosis), celiac disease, thyroid disorders, mononucleosis and reduced blood flow to the liver.

A value inside the lab range but above Gabriel's optimal range can be an early signal of fatty liver, alcohol or a supplement effect. Women's healthy ALT runs lower than men's, which is why Gabriel uses a separate range for each.

The ALT and AST pattern

Clinicians compare AST to ALT. The ratio is a clue, not a diagnosis:

• ALT higher than AST (ratio below 1) is the usual pattern with fatty liver.
• AST about twice ALT or more (ratio above 2) can point toward alcohol-related liver injury.
• AST high with a normal or only slightly high ALT after exercise often reflects muscle rather than liver. A creatine kinase (CK) test can help sort this out.

See AST blood test for more on the ratio and why AST is less liver-specific.

What a low ALT can mean

A low ALT is uncommon and usually not a cause for concern. Very low values can go with low vitamin B6 or chronic kidney disease, so a clinician may look at those if the number is persistently low.

What to do with a high result

1. Read it with the rest of the liver panel. AST, alkaline phosphatase, bilirubin and albumin show whether the pattern looks like liver cell irritation, a bile flow problem or something else.
2. Bring a full list of medications, supplements and pain relievers you take, plus your alcohol intake and any hard workouts in the days before the draw.
3. Ask about the follow-up tests that fit. For a persistent mild rise these often include hepatitis B and C screening, a fasting glucose or A1C and lipids, iron studies with ferritin, and sometimes a liver ultrasound.
4. Recheck after a change. ALT can shift from one draw to the next, so one borderline value is worth confirming. Avoid hard exercise for a few days before a retest.

See a clinician promptly if a high ALT comes with yellowing of the skin or eyes, dark urine, pale stools, pain in the upper right belly, vomiting, unusual confusion or sleepiness, or if you have taken more acetaminophen than the label allows.