Liver Function Panel Updated Apr 17, 2026

Alanine Aminotransferase (ALT)

Alanine Aminotransferase (ALT) is an enzyme measured on a blood test, most often as part of a Liver Panel. ALT on a lab report helps describe how much of this enzyme is present in the bloodstream and is commonly reviewed with other liver-related markers. It is reported as a number in units per liter, and the Alanine Aminotransferase normal range can vary by lab method and reference group.

What Is Alanine Aminotransferase (ALT)?

Alanine Aminotransferase (ALT) is an enzyme measured on a blood test, most often in a Liver Panel. ALT is found mainly inside liver cells, with smaller amounts in other tissues, and the ALT test reports how much of it is present in the blood. On an Alanine Aminotransferase on a lab report, the number helps describe whether the measured level is within the normal Alanine Aminotransferase range used by that laboratory.

Why Is Alanine Aminotransferase (ALT) Tested?

ALT is commonly included in a Liver Panel, Comprehensive Metabolic Panel (CMP), and sometimes other chemistry panels ordered for general health review. The Alanine Aminotransferase test helps show how the blood sample compares with other liver-related markers such as AST, alkaline phosphatase (ALP), bilirubin, albumin, and total protein. ALT on a blood test is often used to build a broader picture of how the sample’s chemistry fits the lab’s reference pattern. In routine reporting, ALT is one of the more commonly reviewed numbers on a lab report.

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Alanine Aminotransferase (ALT) Normal Range

Group Range Unit
Adult Male 7–55 U/L
Adult Female 7–45 U/L

Reference ranges may vary by laboratory and individual factors.

What Does High ALT Mean?

A high ALT means the blood sample contains more Alanine Aminotransferase than the lab’s reference pattern expects. In general, high ALT can reflect release of the enzyme from liver cells into the bloodstream, so the Alanine Aminotransferase test result is often read as a marker of cell injury or stress. Values above a lab’s upper limit, such as above about 35 U/L in adult males or 25 U/L in adult females, are typically considered elevated, although ranges differ by lab. A high ALT on a lab report is usually reviewed together with other numbers rather than by itself.

Associated factors

Recent strenuous exercise — muscle stress can be associated with a temporary high ALT test result.
Alcohol intake — recent alcohol use can influence the ALT number on a blood test.
Certain medications — some drugs can shift the ALT test result upward through liver cell stress.
Higher body weight — body composition changes can be associated with a high ALT reading.
Fatty meal patterns — long-term diet patterns can influence liver-related enzyme release.
Hydration changes — low fluid intake can concentrate blood components and make ALT appear higher.
Smoking — tobacco exposure can be associated with small shifts in ALT values.
Natural sex variation — adult males often have a higher Alanine Aminotransferase normal range than adult females.
Time of day — minor day-to-day shifts can change an ALT test result slightly.

What Does Low ALT Mean?

A low ALT means the measured enzyme level is below the lab’s expected Alanine Aminotransferase reference range. Low ALT is usually less specific than high ALT and often reflects lower enzyme release into the blood sample rather than a single clear pattern. Very small values, such as below about 7 U/L in some adult reference systems, may be flagged as low depending on the lab. On an Alanine Aminotransferase on a blood test, a low result is generally interpreted alongside the rest of the panel.

Associated factors

Low overall protein intake — reduced nutrient intake can be associated with a low ALT number.
Vitamin B6 intake changes — ALT activity depends on vitamin B6-related chemistry.
Low muscle mass — smaller body size can be associated with a low ALT test result.
Older age — age-related shifts can move ALT values toward the low end of the range.
Laboratory method differences — some assays read lower than others for the same sample.
Pregnancy-related dilution — added plasma volume can lower the measured ALT concentration.
Large recent fluid intake — dilution can make ALT appear low on the report.
Normal biologic variation — some people naturally sit below the middle of the Alanine Aminotransferase normal range.
Certain supplements — some supplements can change how ALT is measured or expressed.

How Alanine Aminotransferase (ALT) Relates to Other Values

ALT is often reviewed with AST, alkaline phosphatase (ALP), bilirubin, albumin, and total protein on a Liver Panel. ALT and AST are both enzymes, but they are interpreted together because the pattern can show whether the sample has more enzyme leakage from cells. ALT with ALP and bilirubin helps compare enzyme activity with pigment handling in the same blood draw. When Alanine Aminotransferase on a lab report is viewed with albumin and total protein, the combination adds context about overall blood chemistry.

What Factors Affect Alanine Aminotransferase (ALT) Levels?

ALT can vary by age, sex, body size, and overall muscle mass. The Alanine Aminotransferase reference range may also differ by lab method, analyzer, and population used to set the range. Hydration status, recent exercise, alcohol intake, and time of day can shift an Alanine Aminotransferase test result slightly. A normal Alanine Aminotransferase result in one lab may be outside range in another because reference intervals are not fully standardized. Geographic and population differences can also affect how the lab defines a normal ALT level.

How It Is Tested

The ALT test is done on a blood sample, usually drawn from a vein in the arm. The laboratory measures enzyme activity or concentration and reports the Alanine Aminotransferase test result in units per liter (U/L). On a blood test, ALT is typically listed as a single numeric value with the lab’s reference range beside it.

How to Prepare

No fasting is usually required for the ALT test when it is ordered as part of a Liver Panel. The result can still vary with recent exercise, alcohol, and other routine factors.

Frequently Asked Questions

What is the normal range for Alanine Aminotransferase?
The normal range for ALT depends on the laboratory and the method used. A commonly cited Alanine Aminotransferase normal range is about 7 to 55 U/L for adult males and 7 to 45 U/L for adult females. The reference interval printed on the lab report is the best match for that specific ALT test.
What does ALT stand for?
ALT stands for Alanine Aminotransferase. It is an enzyme reported on a blood test, often in a Liver Panel. On a lab report, ALT is usually shown as a number with units like U/L.
What does a high Alanine Aminotransferase mean on a lab report?
A high ALT means the measured enzyme level is above the lab’s reference range. High ALT is often read as a marker that liver cells may be releasing more enzyme into the bloodstream. The exact meaning depends on how high the ALT test result is and what other values are listed on the same report.
What does a low Alanine Aminotransferase mean on a lab report?
A low ALT means the measured value is below the lab’s expected range. Low ALT is usually less specific than high ALT and often reflects lower enzyme activity or dilution of the sample. The result is best read with the rest of the Liver Panel.
Can hydration affect Alanine Aminotransferase?
Yes, hydration can affect ALT slightly because fluid balance changes how concentrated the blood sample is. A dehydrated sample may make ALT look higher, while a more diluted sample may make it look lower. These shifts are usually small compared with true changes in ALT.
What is the difference between Alanine Aminotransferase and AST?
ALT and AST are both enzymes commonly listed on a Liver Panel, but they are not the same marker. ALT is more focused on liver cell enzyme release, while AST is also found in other tissues. Looking at ALT and AST together gives more context than either value alone.
What unit is Alanine Aminotransferase measured in?
ALT is usually measured in units per liter, written as U/L. That is the standard unit shown on most blood test reports. Some labs may format the ALT test result slightly differently, but U/L is the most common.
How much can Alanine Aminotransferase change between tests?
ALT can change a little from test to test because of normal day-to-day variation and lab method differences. Small shifts within or near the Alanine Aminotransferase normal range are common. Larger changes are more likely when something temporarily affects the sample or the body’s enzyme release.
Is Alanine Aminotransferase different for men and women?
Yes, the Alanine Aminotransferase reference range is often different for adult males and adult females. Many labs use a slightly higher upper limit for men than for women. This is why the reference range printed beside the ALT result matters.
Why is Alanine Aminotransferase tested in a Liver Panel?
ALT is included in a Liver Panel because it helps describe the pattern of liver-related enzymes in one blood sample. When ALT is read with AST, ALP, bilirubin, albumin, and total protein, the panel gives a broader picture of blood chemistry. The ALT test is one piece of that overall lab report.
What does ALT mean on a blood test?
ALT on a blood test means Alanine Aminotransferase was measured in the blood sample. The result is reported as a number with units, usually U/L, and compared with the lab’s normal Alanine Aminotransferase range. That comparison helps show whether the ALT value is within the expected interval for that lab.

Disclaimer

This content is for informational and educational purposes only. It is not intended as medical advice, diagnosis, or treatment recommendation. Reference ranges may vary by laboratory. Always discuss your results with a qualified healthcare professional.

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