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ALT is an enzyme found mainly in your liver. A high level can point to liver damage. A low level is unusual and can be a reason for your doctor to look into it further.[1]
On this page you can read what ALT is, what the guidelines say about a value that is too low or too high, what affects your value and which other values are best to look at alongside it.
Also called: alanine aminotransferase, alanine transaminase, SGPT. At the lab: GPT.
ALT stands for alanine aminotransferase. It is an enzyme: a protein that speeds up certain chemical reactions in your body. It is found mainly in your liver.[1]
Normally there is little ALT in your blood. If liver cells are damaged, ALT is released into your bloodstream. Because ALT is found mainly in the liver, this test looks fairly specifically at liver damage.[1]
The test is usually done together with other liver tests. These measure various proteins, substances and enzymes that show how well your liver is working.[1]
An ALT test is often part of a routine blood check to see how healthy your liver is. The test can also help detect or monitor liver problems.[1]
Some liver conditions already cause a high ALT before you notice anything. That is why the test can help to spot such problems early.[1]
A doctor may also order the test if you have symptoms such as nausea, poor appetite, tiredness, yellow skin or yellow eyes, dark urine or a lot of itching. Or if you have a higher risk, for example because of liver conditions in your family, problematic alcohol use, being very overweight or certain medicines.[1]
ALT can help tell the difference between sudden and long-term liver problems. How high your ALT is does not, however, tell you how much damage your liver has.[1]
Labplusarts, the lab BioProfile works with, uses a reference value of 0 to 45 u/l for ALT (GPT). The lab calls a level between those limits normal.[2]
| Value | What it can mean | Who it is for |
|---|---|---|
| 0 to 45 u/l[2] | The lab calls this normal | ALT (GPT) measurements at this lab |
Source: Labplusarts, the lab BioProfile works with. Reference value for ALT (GPT) measured in this lab.[2]
A lower ALT than usual is not common. Your doctor may then do more tests, because it can point to a vitamin B6 deficiency or a long-term kidney condition.[1]
A higher ALT than usual can point to liver damage. This can be caused by inflammation of the liver, other liver conditions, too little blood supply to the liver, certain medicines such as cholesterol medicines or painkillers, or toxic substances. A high level does not always mean there is a condition that needs care. Talk to your doctor about what your result means for you.[1]
BioProfile is working on its own zones for each value, from risk to optimal. A doctor reviews those zones before they appear in your result.
Certain medicines and dietary supplements can affect your result. Tell your doctor what you take. Never stop a medicine on your own, only when your doctor tells you to.[1]
Heavy physical exertion can affect your ALT.[1]
Your age, sex and weight also play a part. Your ALT can also vary depending on where you are in your menstrual cycle.[1]
ALT is usually measured together with other blood tests. For these, you often need to fast for a few hours. Your healthcare provider will tell you if there are any special instructions.[1]
ALT is included in BioProfile 77, 98, 121 and 150.[3]
The BioProfile editorial team wrote this page on 8 October 2026 from the sources below, which we read on 8 October 2026. Every number on this page appears in one of those sources, with the number of that source next to it. An expert will still review this page; after that review, the expert's name and the date of the review will appear at the top. This page offers explanation, not a diagnosis. Discuss an abnormal level with your GP.
