Alanine Aminotransferase (ALT)
An enzyme made mostly in liver cells. It leaks into the blood when liver cells are irritated or damaged.
AI-verified against cited sources. Awaiting expert reviewAlso called ALT, SGPT, GPTLOINC 1742-6
Check your result
The usual range for ALT depends on sex. Choose female or male above to see where you stand.
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What it is
ALT (alanine aminotransferase) is an enzyme that helps your cells process amino acids and make energy. Most of it sits inside liver cells, with smaller amounts in muscle and other tissues. When liver cells are irritated or damaged, some ALT leaks into the blood, where this test can measure it. It is one of the most common liver blood tests and is usually reported with AST, ALP and bilirubin.
Why it matters
ALT is a sensitive sign that liver cells are under stress, sometimes before you feel any symptoms. A raised ALT is common, and many causes are temporary or treatable, such as fatty liver, alcohol, medicines or a hard workout. A result in the usual range doesn't prove the liver is healthy, because some long-term liver conditions don't raise ALT. Large studies also link ALT that is on the high side but still inside the lab's range to more liver-related deaths over time, which is why some guidelines use lower limits than many labs.
If it’s low
A low ALT on its own usually isn't a concern. MedlinePlus notes that lower-than-usual ALT is not common and lists low vitamin B6 (which the enzyme needs to work) and chronic kidney disease as possible reasons, so your clinician may look at your other results.
Common causes
- Normal variation, since some healthy people have low values
- Low vitamin B6, which the enzyme needs to work (for example with heavy alcohol use)
- Chronic kidney disease
- Sulfasalazine, which can falsely lower results on some lab instruments
What can help
- Nothing specific is needed for a low result by itself
- If you are curious, ask whether anything else in your results suggests a reason to look further
If it’s high
A raised ALT means more of the enzyme is leaking into your blood than usual, most often from the liver and sometimes from muscle. Mild rises (under about five times your lab's upper limit) are the most common, and they often have a temporary or treatable cause. Very high levels are less common and more often tied to a sudden injury to the liver, so clinicians look at them more urgently.
Common causes
- Hard exercise or weightlifting, which can raise ALT for several days
- Fatty liver disease (MASLD, formerly called NAFLD), which is linked to extra body fat, high blood sugar and high triglycerides
- Regular alcohol use
- Medicines, supplements and herbal products, including acetaminophen taken in high doses
- Viral infections that reach the liver, such as hepatitis A, B or C, and illnesses like mononucleosis
- Less common causes: autoimmune liver disease, iron overload (hemochromatosis), Wilson disease, celiac disease or an overactive thyroid
What can help
- Tell your clinician about every medicine, supplement and herbal product you take, and ask whether any could affect your liver
- If you drink alcohol, ask how much is reasonable for you; heavy drinking speeds up liver injury
- If fatty liver is the cause, steady weight loss (about 3-5% of body weight improves liver fat, and more than 10% is generally needed to improve inflammation and scarring) and regular exercise help
- If you did unusually hard exercise recently, mention it and ask whether to repeat the test after a rest
- Ask whether other tests, such as AST, bilirubin, hepatitis tests or an ultrasound, would help put your result in context
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
The usual range depends on sex and age. Choose women or men to see the one that applies.
- Men, 18+0–44 U/L
Sources: Labcorp, Hepatology, Mayo Clinic Laboratories, American Board of Internal Medicine, MedlinePlus, National Library of Medicine
- Women, 18+0–32 U/L
Sources: Labcorp, Hepatology, Mayo Clinic Laboratories, American Board of Internal Medicine, MedlinePlus, National Library of Medicine
See ALT by age and sex, with the U.S. survey numbers where they exist.
Wellness targets
Narrower ranges some clinicians aim for. Being outside one doesn’t mean something is wrong.
up to 33 U/L (Men, 18+). Evidence: Moderate. Two U.S. liver guidelines say a truly healthy ALT in men is about 29 to 33 U/L, below many lab limits, and large cohorts link ALT even inside the lab range to more liver-related deaths. This is a statistical limit from low-risk groups, not a trial-proven target, so the top of the span is used here.
up to 25 U/L (Women, 18+). Evidence: Moderate. Two U.S. liver guidelines say a truly healthy ALT in women is about 19 to 25 U/L, below many lab limits, and large cohorts link ALT even inside the lab range to more liver-related deaths. This is a statistical limit from low-risk groups, not a trial-proven target, so the top of the span is used here.
If this applies to you
ALT means a little more for some people. Open the one that fits you.
Celiac disease or IBD
Raised liver enzymes can be part of untreated celiac disease, often without symptoms, and ACG suggests that people with unexplained raised liver enzymes be checked for celiac disease. These gluten-related rises return to normal on a gluten-free diet in most people.
Gout
The allopurinol label lists liver tests, including ALT, among the tests to check before starting it for gout. It suggests checking liver enzymes from time to time in people who already have liver disease.
High cholesterol or heart risk
ALT is a liver enzyme. The atorvastatin (Lipitor) label suggests considering liver enzyme tests before starting, and after that when there is a clinical reason.
Hemochromatosis or iron overload
Iron builds up mainly in the liver, so liver enzymes are part of the first workup. EASL notes that with ferritin under 1,000 µg/L (the same as 1,000 ng/mL), normal liver enzymes and no enlarged liver, the chance of advanced liver scarring is very low.
Fatty liver or liver condition
ALT is the most liver-specific of the liver enzymes, BSG notes. AASLD notes that the upper limits most labs print are higher than a true normal in fatty liver disease, and that ALT and AST are often in the usual range even with advanced scarring.
Tracking for long-term health
ALT is a liver enzyme on standard blood panels, and it is often ordered with GGT and other liver tests. Hard exercise before a test is one of the things MedlinePlus lists as able to change lab results.
Prediabetes or diabetes
ALT is a liver enzyme and one of the inputs to FIB-4. The ADA notes that relying on a raised ALT would miss most people with the inflamed form of fatty liver disease. When ALT stays high for more than 6 months with a low FIB-4, the ADA suggests looking for other liver causes.
Strength training
ALT is usually read as a liver test, but heavy workouts can raise it too. An Endocrine Society statement notes that liver enzymes raised by heavy workouts can be misread as a sign of liver problems.
Taking isotretinoin
Liver enzymes rose in some people in clinical trials, and hepatitis has been reported. The label asks for liver tests before starting and from time to time until the response is known. A 2022 panel of acne experts agreed on ALT as the liver test to check, and not GGT or bilirubin.
Taking methotrexate
Methotrexate can affect the liver, so liver enzymes are checked before starting and regularly after. The British Society for Rheumatology (BSR) suggests ALT, AST or both at every routine check.
How common is your level?
NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.
Use the left and right arrow keys to read each age. Shift moves five years.
Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles 2015-2016, 2017-March 2020 (pre-pandemic), August 2021-August 2023. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.
Explore ALT by age and sex: every percentile as a table, with a download.
What can affect your result
- Sex: levels are usually higher in men than in women
- Age: labs use lower limits for children and teens
- Body fat, blood sugar and blood fats: more body weight and metabolic changes go with higher ALT
- Hard exercise, especially weightlifting, which can raise ALT for about a week
- Alcohol, medicines and supplements
- Where you are in your menstrual cycle
- Lab method: tests that add vitamin B6 to the reaction read slightly differently from tests that don't
- Hard exercise, especially weightlifting, can raise ALT (and AST) for a week or more. If you want a baseline value, ask your clinician whether to avoid unusually hard workouts for a few days before the draw.
- Hemolysis (red blood cells breaking open in the tube) can falsely raise results, because red cells hold several times more ALT than serum does.
- Some medicines and supplements raise ALT in the body, including high-dose acetaminophen and certain herbal products. Tell your clinician about everything you take.
- Sulfasalazine can falsely lower results on some Beckman Coulter instruments, according to Quest Diagnostics.
- Low vitamin B6 (pyridoxal phosphate) can lower measured ALT, and methods that add B6 to the reaction read slightly differently from methods that don't.
Falls over days to weeks once a short-term cause (such as a hard workout or a medicine) is removed, since ALT's half-life in blood is about 47 hours. Changes from weight loss or other lifestyle changes take longer to show.
When to talk to a clinician
Get urgent care for yellow skin or eyes, very dark urine, pale stools, severe belly pain, vomiting that won't stop, or confusion or unusual sleepiness, especially with a high ALT. Talk with a clinician soon if your ALT is above about five times your lab's upper limit (roughly 250 U/L or more), if it keeps rising, or if a raised result comes with tiredness, nausea or pain in the upper right belly. A smaller rise with no symptoms can usually be raised at your next visit.
Questions you could ask
- How does my ALT compare with my earlier results?
- Which upper limit do you use for me, my lab's or a lower healthy-liver one?
- Could any of my medicines, supplements or alcohol use be affecting this result?
- Should we repeat the test, and when?
- Would other tests, such as AST, bilirubin, ALP or an ultrasound, help put this in context?
- Could a recent hard workout explain this?
Questions people ask
Why does my lab's upper limit differ from what guidelines call a healthy ALT?
Most labs set their limits using groups of people that included some with unrecognized fatty liver or other liver stress, which pushes the limit up. Labcorp prints up to 44 U/L for men and 32 for women, and Mayo Clinic Laboratories 55 and 45. The American College of Gastroenterology and AASLD say a healthy ALT tops out nearer 29 to 33 U/L in men and 19 to 25 in women. Both views are in use, so ask your clinician which one fits your situation.
Can a hard workout raise my ALT?
Yes. In one study of healthy men, an hour of weightlifting raised ALT and AST for at least a week, and the muscle enzyme CK rose much more. If ALT is your only raised liver test and you recently lifted weights or did an unusually hard workout, tell your clinician. They may suggest repeating the test after a rest.
If my ALT is in the usual range, does that mean my liver is fine?
Not always. ALT can be in the usual range in some people with long-term liver conditions, including some with fatty liver or scarring. It is one clue, and clinicians also look at your history, other blood tests and sometimes imaging.
What is the difference between ALT and AST?
Both are enzymes that leak out of stressed liver cells. ALT is found mostly in the liver, while AST is also found in other tissues such as muscle and heart, so ALT points more specifically to the liver. Clinicians often compare the two.
How do I convert ALT between U/L and µkat/L?
For ALT, U/L and IU/L are the same number. To get µkat/L, divide U/L by 60 (or multiply by 0.0167). For example, 36 U/L is 0.60 µkat/L. To go the other way, multiply µkat/L by 60.
Show the science and sources
Units
- 1 U/L = 1 U/L
- 1 U/L = 0.01667 µkat/L
- 1 U/L = 16.67 nkat/L
Is a change real?
ALT naturally varies about 9.3% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 32% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: The European Biological Variation Study (EuBIVAS): a summary report.
For clinicians and researchers
ALT is a cytosolic transaminase that moves an amino group from alanine to alpha-ketoglutarate, producing pyruvate and glutamate, and it needs pyridoxal-5'-phosphate (P-5'-P, vitamin B6) as a cofactor. It is concentrated in hepatocytes, so it is more liver-specific than AST. Its circulating half-life is about 47 hours (AST about 17 hours), and P-5'-P deficiency lowers measured activity more for ALT than for AST. Results are enzyme activity concentrations that depend on method, temperature and whether P-5'-P is added (LOINC 1743-4 with, 1744-2 without), so reference limits differ between labs. Many lab limits come from reference groups that included people with subclinical liver disease. ACG (2017) and AASLD (2023) cite a healthy ALT of 29-33 U/L in men and 19-25 U/L in women, and ALT inside the lab range still tracks liver-related mortality in large cohorts. Magnitude is often graded as mild (under 5 times the upper limit), moderate (5-10 times) or marked (over 10 times), though no uniform definition exists, and levels above about 75 times the upper limit point to ischemic or toxic injury in over 90% of acute cases. A normal ALT does not exclude chronic hepatitis, fatty liver with fibrosis or cirrhosis.
LOINC 1742-6 (primary), 1743-4, 1744-2, 77144-4. Specimen: serum-or-plasma.
Sources
- Pediatric Testing Reference Ranges (ALT (SGPT), test 001545; lists ages 0 to 17 and adults over 17), Labcorp
- Alanine Aminotransferase (ALT/SGPT) (test 001545), Labcorp
- Comprehensive Metabolic Panel, Serum (test CMAMA), Mayo Clinic Laboratories Extended Catalog, Mayo Clinic Laboratories
- Alanine Aminotransferase, Serum or Plasma (test 0020008), ARUP Laboratories
- Alanine Aminotransferase (ALT) (test code 823), Quest Diagnostics
- ABIM Laboratory Test Reference Ranges, January 2026, American Board of Internal Medicine (2026)
- ALT blood test (MedlinePlus Medical Encyclopedia), MedlinePlus, National Library of Medicine
- ALT Blood Test (MedlinePlus Lab Tests), MedlinePlus, National Library of Medicine
- 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, Hepatology (2023)
- Updated definitions of healthy ranges for serum alanine aminotransferase levels, Annals of Internal Medicine (2002)
- Upper limits of normal for alanine aminotransferase activity in the United States population, Hepatology (2012)
- Normal serum aminotransferase concentration and risk of mortality from liver diseases: prospective cohort study, BMJ (2004)
- Liver enzyme alteration: a guide for clinicians, Canadian Medical Association Journal (2005)
- Mildly elevated liver transaminase levels in the asymptomatic patient, American Family Physician (2005)
- Muscular exercise can cause highly pathological liver function tests in healthy men, British Journal of Clinical Pharmacology (2008)
- LOINC codes for alanine aminotransferase (NLM Clinical Tables search), National Library of Medicine
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.