ALT (SGPT) Blood Test: Normal Range and High ALT Causes

TL;DR

• ALT (alanine aminotransferase, also called SGPT) is an enzyme found mainly in the liver, which makes it the more liver-specific of the two common liver enzymes.
• Lab ranges often run up to about 36–56 U/L, but liver experts consider a healthy ALT to be about 29–33 U/L for men and 19–25 U/L for women. A result your lab calls normal can sit above that.
• The most common cause of a mildly high ALT is fatty liver. Alcohol, medicines and supplements, viral hepatitis, celiac disease and muscle injury are others.

An ALT blood test measures alanine aminotransferase, an enzyme made mostly in liver cells, so a high ALT is a fairly specific sign that your liver is irritated. Many labs list a normal range up to about 36 U/L, but liver experts consider a truly healthy ALT to be lower: about 29–33 U/L in men and 19–25 U/L in women.

Mildly raised ALT is common, and serious liver disease behind it is uncommon. This guide explains how to read your number, what the sex differences mean, the common causes of high ALT, what a low ALT means and what brings it down. You can enter your result into the checker above to compare it with both the typical lab limit and the healthy limits for your sex.

What Does My ALT Number Mean?

Doctors read ALT as a multiple of the upper limit of normal on your report. The American College of Gastroenterology (ACG) uses these grades:

Your ALT vs. your lab’s upper limit	Example if the limit is 36 U/L	What it usually means
At or below the limit	36 or less	Normal by the lab, but it may still be above the healthy limit for your sex
Up to 2× the limit (borderline)	37–71	Very common. Fatty liver is the usual suspect; alcohol, medicines and exercise are others. Usually rechecked
2–5× the limit (mild)	72–180	Worth a full look for the cause with your doctor
5–15× the limit (moderate)	181–540	The ACG says this needs immediate evaluation
More than 15× the limit (severe)	Above 540	Seen with acute viral hepatitis, drug or toxin injury (such as acetaminophen) or poor blood flow to the liver. Needs urgent medical care

Labs set their own reference ranges, so the range printed on your report always wins over any example here. A single result is never a diagnosis: your doctor will look at the trend and your other results.

What Is ALT (SGPT)?

ALT is an enzyme inside cells that helps process amino acids. When liver cells are damaged or stressed, some of it leaks into the blood. Older reports call it SGPT (serum glutamate pyruvate transaminase); it’s the same test.

What makes ALT useful is where it lives. The ACG guideline explains that ALT is present primarily in the liver and is therefore a more specific marker of liver cell injury than AST, which is also found in heart muscle, skeletal muscle, kidney and brain. That’s why doctors read the two together. For the other enzyme, see our guide to the AST blood test.

What Is a Normal ALT Level for Women and Men?

This is where lab reports and liver experts often disagree.

Yardstick	Women	Men
Example lab range (MedlinePlus)	4–36 U/L	4–36 U/L
Example lab range (Cleveland Clinic)	7–56 U/L	7–56 U/L
ACG “true healthy” upper limit	19–25 U/L	29–33 U/L
AASLD line suggesting chronic liver injury	Above 30 U/L for 6–12 months	Above 30 U/L for 6–12 months

U/L and IU/L mean the same thing on lab reports.

Why the gap? Lab ranges are often built from local reference groups that may include people with undiagnosed fatty liver, often without accounting for body weight, and ALT rises with weight. The ACG’s healthy limits come from studies that screened those people out. In one, of 6,835 blood donors with normal weight and no hepatitis, the upper limit came out at 30 U/L for men and 19 U/L for women.

A few things to know if you searched “ALT normal range female”:

• ALT is naturally higher in men, so a single cutoff for everyone is generous to women.
• The healthy range catches a lot of people. The ACG notes that applying limits of 29 U/L for men and 22 U/L for women to US national survey data would label 36% of men and 28% of women as having elevated ALT.
• It matters for health. The ACG cites studies from the US and Korea linking higher ALT to higher liver-related mortality; one US analysis used limits of 30 U/L for men and 19 U/L for women.

Reading common results: ALT 24, 36, 38 and 66

Your ALT	Against a 36 U/L lab limit	Against the ACG healthy limit
24	Normal	Below the limit for men; at the top edge of the healthy range for women
36	At the top of the range; may not be flagged	Above the healthy limit for both sexes and above the AASLD’s 30 U/L line
38	Just over (about 1.1×): borderline	Above for both sexes
66	About 1.8×: borderline	More than 2.5 times the healthy limit for women; about twice it for men

None of these is an emergency on its own. But results like 36, 38 or 66 that stay put over months are worth a conversation, especially if you have extra weight, diabetes or high blood pressure.

What Causes High ALT?

• Fatty liver. MASLD (metabolic dysfunction-associated steatotic liver disease, formerly NAFLD; here’s what the new name means) is the most common cause of raised liver enzymes without symptoms. A systematic review cited in American Family Physician found it behind 25% to 51% of such cases of raised ALT or AST, depending on the group studied. In fatty liver, ALT is usually higher than AST and rarely above 300 U/L. Our pillar guide to ALT and AST levels in fatty liver goes deeper.
• Alcohol, on its own or on top of fatty liver.
• Medicines and supplements. Acetaminophen can raise ALT even at therapeutic doses, and supplements now cause 9% of drug-induced liver injury cases, according to the same review. Statin-related liver injury is rare.
• Viral hepatitis, especially hepatitis B and C, which your doctor can check for with blood tests.
• Celiac disease, which can cause modest rises. The ACG suggests screening for it when enzymes stay high without another explanation.
• Less common liver conditions, including hemochromatosis (iron overload), autoimmune hepatitis, Wilson disease and alpha-1 antitrypsin deficiency.
• Thyroid disease, both underactive and overactive.
• Muscle injury or very hard exercise, which mainly raise AST but can lift ALT too.

Why Is My ALT High but AST Normal?

This is a liver-pointing pattern. In the ACG guideline, conditions where ALT is generally higher than AST include fatty liver, chronic and acute viral hepatitis, medicine and supplement injury, and celiac disease. Because muscle and the heart contain relatively little ALT, a raised ALT with a normal AST makes a non-liver source less likely.

When AST pulls ahead of ALT instead, the list of possible causes changes. Our guide to the AST/ALT ratio explains what that pattern can mean.

What Does a Low ALT Mean?

A low ALT is uncommon and usually isn’t a cause for concern, according to Cleveland Clinic, which links it to vitamin B6 deficiency and chronic kidney disease. In older adults, research has linked very low ALT with frailty and loss of muscle mass, so it’s best thought of as a general health clue rather than a liver problem.

How Can I Lower My ALT?

ALT comes down when its cause is dealt with. Since fatty liver is the most common reason, the levers that reduce liver fat are the ones that usually move ALT:

• Lose some weight if you carry extra. The AASLD guidance says weight loss of 3–5% improves liver fat, while more than 10% is generally needed to improve inflammation (MASH) and scarring. It also notes that ALT returning to normal can predict MASH resolution after lifestyle changes. See how to reverse fatty liver for a step-by-step plan.
• Cut back on alcohol. It adds to liver injury on top of fatty liver.
• Review medicines and supplements with your doctor, including herbal products and pain relievers. Don’t stop a prescribed medicine on your own.
• Treat other causes. Hepatitis B and C can be treated, and in celiac disease raised enzymes usually return to normal within about a year on a strict gluten-free diet.

Daily food choices add up here. An app like Liverly can score your meals so you can see which habits, like sugary drinks, are worth changing first.

Should I Retest a High ALT?

Usually. The ACG recommends repeating the test or doing a clarifying test before a full workup, to confirm the result is truly abnormal. Before the retest, skip unusually hard workouts for about a week, go easy on alcohol, and bring a list of everything you take.

Good questions for your doctor:

• Is my ALT above the healthy limit for my sex, even if the lab didn’t flag it?
• What was my AST, and which is higher?
• Have hepatitis B and C, medicines, iron overload and celiac disease been considered?
• Do I need an ultrasound, a FIB-4 score or a FibroScan?

For how ALT fits with the rest of your panel, including ALP, GGT and bilirubin, see our guide to liver function test results.

The Bottom Line

ALT is the more liver-specific of the two main liver enzymes, so a high ALT is a real signal that your liver is irritated, though usually mildly. Lab ranges are often generous; liver experts consider about 29–33 U/L healthy for men and 19–25 U/L for women. Fatty liver is the most common cause, and weight loss, less alcohol and a medicine review are the usual fixes. Track your trend, ask what’s behind a persistent rise, and get prompt care for any result more than 5 times the limit.

Sources

• Kwo et al. ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries (American Journal of Gastroenterology 2017)
• AASLD Practice Guidance on the clinical assessment and management of nonalcoholic fatty liver disease (Rinella et al., Hepatology 2023)
• Oh et al. Mildly Elevated Liver Transaminase Levels: Causes and Evaluation (American Family Physician 2017)
• MedlinePlus: Alanine transaminase (ALT) blood test
• Cleveland Clinic: Alanine Transaminase (ALT) Blood Test

This article is for informational purposes only and is not medical advice. Talk to your doctor or hepatologist about your specific situation.