ALT (SGPT) is a liver enzyme measured through a simple blood test. ALT stands for alanine aminotransferase, and SGPT (serum glutamic-pyruvic transaminase) is an older name for the same thing. This enzyme lives primarily inside your liver cells, where it helps break down proteins into energy. When liver cells are damaged or inflamed, ALT leaks into your bloodstream, and the amount detected on a blood test tells your doctor how much stress your liver is under.
What ALT Actually Does in Your Body
ALT is a workhorse enzyme involved in amino acid metabolism. It transfers a chemical group between molecules, a process that helps your liver convert food into usable energy. Small amounts of ALT circulate in your blood normally, but the vast majority stays locked inside liver cells. That’s what makes it such a useful marker: a spike in blood levels is a strong signal that something is irritating or injuring the liver itself.
ALT needs vitamin B6 to function properly. Specifically, it relies on a form of B6 called pyridoxal 5′-phosphate as a helper molecule. Without enough B6, the enzyme can’t do its job, and measured ALT levels may appear artificially low. This matters because a person with a B6 deficiency and genuine liver damage could get a misleadingly normal-looking result, causing the damage to be underestimated.
Normal ALT Ranges
Normal ALT levels typically fall between 7 and 56 IU/L (international units per liter), though reference ranges vary slightly between labs. Men generally run higher than women, and results can shift based on age, body weight, and muscle mass. If your result falls within the range printed on your lab report, your liver is likely functioning normally. A result slightly above that range doesn’t automatically mean you have liver disease, but it does warrant a closer look.
A single elevated reading isn’t a diagnosis. Doctors often repeat the test after a few weeks to see whether the number comes back down on its own or stays elevated, which helps separate a temporary spike from an ongoing problem.
Common Causes of High ALT
Elevated ALT points to liver cell damage, but the list of things that can cause that damage is long. The most common culprits include:
- Fatty liver disease (MASLD): The leading cause of mildly elevated ALT worldwide, driven by excess weight, insulin resistance, or metabolic syndrome. Some people with fatty liver still show normal ALT, so a normal result doesn’t completely rule it out.
- Hepatitis: Viral infections (hepatitis A, B, or C) can cause ALT to spike dramatically, sometimes into the hundreds or thousands.
- Alcohol-related liver disease: Chronic heavy drinking inflames and scars liver tissue over time.
- Cirrhosis: Advanced scarring of the liver from any cause, including long-term hepatitis or alcohol use.
- Liver cancer: Tumors in the liver release enzymes into the bloodstream.
- Reduced blood flow to the liver: Heart failure or shock can starve liver cells of oxygen, causing damage.
Infections outside the liver can raise ALT too. Infectious mononucleosis (mono) is a well-known example, since the virus that causes it often inflames the liver temporarily.
Medications That Can Raise ALT
Dozens of common medications are capable of pushing ALT levels up, sometimes without causing symptoms you’d notice. Acetaminophen (the active ingredient in Tylenol) is one of the most frequent offenders, especially at higher doses. Cholesterol-lowering statins, certain blood pressure medications like losartan, common antidepressants including fluoxetine and sertraline, anti-inflammatory painkillers (NSAIDs), and the acid reflux drug omeprazole can all contribute.
Herbal and dietary supplements aren’t risk-free either. Green tea extract, kava, and germander have all been linked to liver cell injury and elevated ALT. If your levels come back high, your doctor will likely review everything you’re taking, including supplements, to rule out a medication-related cause before investigating further.
The AST/ALT Ratio
ALT is often ordered alongside a related enzyme called AST (aspartate aminotransferase). Both rise when the liver is under stress, but the ratio between them can help pinpoint the cause. In most types of acute liver injury, including viral hepatitis and fatty liver disease, ALT tends to be higher than AST, producing a ratio of 1 or below. When the AST/ALT ratio climbs above 2, that pattern is more characteristic of alcohol-related liver damage. It’s not a definitive diagnostic tool on its own, but it gives your doctor a useful clue about what’s driving the problem.
What Symptoms to Watch For
Mildly elevated ALT often produces no symptoms at all, which is why the test is so valuable. Liver damage can quietly progress for years before you feel anything. When symptoms do appear, they tend to reflect more significant or sustained injury: persistent fatigue, abdominal pain or swelling (especially in the upper right side), dark urine, pale stools, nausea, and yellowing of the skin or eyes (jaundice). Unexplained itching is another sign that liver function may be compromised.
Many people first discover elevated ALT on routine blood work done for an unrelated reason, like an annual physical or a pre-surgery screening. That incidental finding is often the earliest warning that something needs attention.
Factors That Affect Your Results
A few things can temporarily push ALT higher without meaning your liver is diseased. Intense exercise, particularly strength training or endurance events, can cause muscle breakdown that releases small amounts of ALT into your blood. Carrying excess body weight raises baseline ALT levels even before fatty liver disease develops. Certain supplements, alcohol consumption in the days before your blood draw, and even a recent illness can all skew results.
If your doctor suspects a temporary cause, they’ll typically ask you to avoid strenuous workouts and alcohol for a few days, then repeat the test. A result that normalizes on its own is reassuring. One that stays elevated, or keeps climbing, usually leads to further testing: imaging of the liver, viral hepatitis screening, or in some cases a referral to a liver specialist.
What Unusually Low ALT Means
Most people worry about high ALT, but very low levels can carry meaning too. A vitamin B6 deficiency is the most common explanation, since ALT depends on B6 to function. Kidney disease can also suppress ALT activity, as can certain rare genetic mutations that affect the enzyme itself. In clinical settings, the concern with abnormally low ALT is that it could mask real liver damage by keeping the number deceptively close to zero when it should be rising. Clinicians working with patients who have known B6 deficiency or chronic kidney disease may use a lower threshold when interpreting results.