ALT (alanine aminotransferase) blood test: what it means
What it measures
The ALT (alanine aminotransferase, also called alanine transaminase) blood test measures the level of the enzyme ALT in your blood. ALT is an enzyme — a protein that helps speed up chemical reactions in the body — found mainly in the liver, and when liver cells are damaged they release ALT into the bloodstream, so the blood level is used as a general marker of liver health.
Why it’s ordered
ALT is commonly measured to help check the health of your liver and to help diagnose or monitor liver injury or disease. It is often part of a routine blood screening and is usually done alongside other liver tests (such as AST, ALP, and bilirubin) rather than interpreted on its own.
General reference range
MedlinePlus's Medical Encyclopedia gives a general normal range of about 4 to 36 U/L (0.07 to 0.60 µkat/L). This is a general guide only: normal value ranges can vary slightly among different labs, and some labs use different measurements or test different samples, and results can also be influenced by factors such as age, sex, and method. Because of this, the reference range printed on your own lab report is the one that applies to your result — a single number should not be read as a personal diagnosis.
If it’s high
A higher-than-usual ALT level may be a sign of liver injury or disease, and it is most meaningful when other liver test values are also raised. As general, hedged possibilities (not a diagnosis and not a complete list), higher levels can be seen with conditions such as hepatitis, infection, cirrhosis, fatty liver, liver tumors or liver cancer, reduced blood flow to the liver, hemochromatosis, mononucleosis, pancreatitis, and the effects of certain medicines or poisons (for example alcohol or acetaminophen). A high ALT does not always mean there is a medical condition that needs treatment.
If it’s low
Lower-than-usual ALT levels are not commonly reported and are generally not a focus of this test. MedlinePlus notes that, when seen, low levels may be associated with things such as vitamin B6 deficiency or chronic kidney disease. This is general information, hedged, and not a diagnosis. Your results are interpreted in the context of your overall health, symptoms, and other tests, and your health care provider is the right person to explain what your specific ALT result means for you. This is general information, not medical advice.
A result is not a diagnosis
Reference ranges vary by laboratory, age, sex, and method — the range on your own report is what applies to you. A single value out of range doesn’t confirm any condition; your clinician interprets it alongside your symptoms, history, and other results. This page is general information, not medical advice.
Medicines that can move this result
The liver turns a small share of each dose into a reactive by-product that it normally neutralises. Even at the full recommended 4 grams a day, taken daily, this is enough to lift ALT in some people — peaks above three times normal in 39% of subjects in the study LiverTox cites — and after an overdose the rise is dramatic.
Source ↗This antibiotic combination is the most common cause of drug-induced liver injury in large case series from North and South America, Australia and Europe. The clavulanate rather than the amoxicillin appears responsible, through an immune-mediated reaction, and onset averages about three weeks — often after the course of tablets has already been finished.
Source ↗A toxic intermediate builds up as the liver breaks isoniazid down, damaging liver cells. Most of these rises are symptom-free and often settle even if treatment continues; liver-test monitoring, usually monthly at first, is recommended for people at higher risk — pre-existing liver disease or age over 50.
Source ↗Mild, symptom-free ALT rises happen in 1% to 3% of people on atorvastatin. Rises past three times the normal ceiling are uncommon — 0.7% versus 0.3% on placebo — and are more likely on bigger doses, reaching 2.3% at 80 mg daily. Most settled on their own without any dose change.
Source ↗On the long-term, low-to-moderate weekly doses used for arthritis and psoriasis, ALT rises are frequent but usually mild. About 5% of patients exceed twice the normal ceiling, and those levels come down quickly if the dose is paused or lowered — sometimes even if the same dose continues. This is why blood tests are scheduled alongside the drug.
Source ↗This seizure and mood medicine commonly produces a mild, symptom-free ALT rise that often fades even while the drug is continued. Clinically apparent liver injury from valproate is a separate and much less common event, but it can be serious, so symptoms matter more than the number alone.
Source ↗Amiodarone is highly fat-soluble and, taken long term, accumulates in tissues including the liver, so the higher the daily dose the more likely ALT is to climb. LiverTox notes these elevations often settle despite continuing the drug, and that people on amiodarone are advised to have ALT and AST checked at baseline and then every six months.
Source ↗Mild aminotransferase rises occur in up to 5% of people on fluconazole and usually resolve even if the drug is continued. A marked rise is uncommon but is the single most frequent adverse event that leads to stopping treatment early; injury, when it happens, typically shows up in the first few weeks.
Source ↗Do not stop a prescribed medicine over a lab number. These are recognised associations, not a finding about your result — your value may have nothing to do with any medicine you take, and the list is not complete. Bring it to whoever prescribed the drug; they can weigh it against why you are taking it.
Frequently asked
- What does the ALT (alanine aminotransferase) blood test measure?
- The ALT (alanine aminotransferase, also called alanine transaminase) blood test measures the level of the enzyme ALT in your blood. ALT is an enzyme — a protein that helps speed up chemical reactions in the body — found mainly in the liver, and when liver cells are damaged they release ALT into the bloodstream, so the blood level is used as a general marker of liver health.
- What is a normal ALT (alanine aminotransferase) blood test range?
- MedlinePlus's Medical Encyclopedia gives a general normal range of about 4 to 36 U/L (0.07 to 0.60 µkat/L). This is a general guide only: normal value ranges can vary slightly among different labs, and some labs use different measurements or test different samples, and results can also be influenced by factors such as age, sex, and method. Because of this, the reference range printed on your own lab report is the one that applies to your result — a single number should not be read as a personal diagnosis.
- What does a high result mean?
- A higher-than-usual ALT level may be a sign of liver injury or disease, and it is most meaningful when other liver test values are also raised. As general, hedged possibilities (not a diagnosis and not a complete list), higher levels can be seen with conditions such as hepatitis, infection, cirrhosis, fatty liver, liver tumors or liver cancer, reduced blood flow to the liver, hemochromatosis, mononucleosis, pancreatitis, and the effects of certain medicines or poisons (for example alcohol or acetaminophen). A high ALT does not always mean there is a medical condition that needs treatment.
- What does a low result mean?
- Lower-than-usual ALT levels are not commonly reported and are generally not a focus of this test. MedlinePlus notes that, when seen, low levels may be associated with things such as vitamin B6 deficiency or chronic kidney disease. This is general information, hedged, and not a diagnosis. Your results are interpreted in the context of your overall health, symptoms, and other tests, and your health care provider is the right person to explain what your specific ALT result means for you. This is general information, not medical advice.
Other lab tests
Sources
General reference, not medical advice, and not a substitute for your clinician. Lab reference ranges and interpretation depend on the laboratory and on your individual situation — discuss your results with a licensed healthcare professional.