Table of ContentsView AllTable of ContentsWhen They’re MeasuredWhat They ShowNormal and High LevelsWhat Can Affect Results?
Table of ContentsView All
View All
Table of Contents
When They’re Measured
What They Show
Normal and High Levels
What Can Affect Results?
Aspartate aminotransferase(AST) andalanine aminotransferase(ALT)are two liver enzymes measured in a blood test to check the health of your liver. High AST and ALT levels are a general sign of a liver problem.
Based on which enzyme is elevated—or if both are elevated—healthcare providers can make an educated guess as to the underlying cause of theliverproblem and order additional tests. This may help diagnose diseases ranging from hepatitis and cirrhosis to liver cancer and liver failure.
Verywell / Elise Degarmo
When ALT and AST Levels Are Tested
ALT andASTare part of a comprehensive panel of tests known as aliver function test (LFT). An LFT may be ordered:
When the liver is damaged, ALT and AST can leak into the bloodstream. High levels of ALT and AST in the blood are reliable markers forliver disease.
What Each Test Can Show
High ALT and AST are strong indications of liver disease, but what they tell us individually and together can be very different. This is because ALT is produced mainly in the liver,while AST is produced in the liver, brain,pancreas, heart,kidneys, lungs, and muscles.
As such, a high ALT is a pretty clear indication of liver disease.On the other hand, a high AST may be a sign of liver disease or conditions affecting the brain, pancreas, heart, kidneys, lungs, or muscles.
ALT and AST are measured in international units per liter (U/L). The normal range of values (meaning the values between which levels are normal) are:
The high end of the reference range is referred to as the upper limit of normal (ULN).
High ALT and AST levels may indicate a problem with your liver, but it doesn’t necessarily mean that you have a condition requiring treatment. This is because there is a wide gap between the ULN and what is considered to be dangerously high levels.
Mild elevations are generally two to three times that of the ULN. With some liver diseases, the level can be more than 50 times that of the ULN. Levels this high are considered to be dangerous.
Very elevated ALT and AST levels can indicate:
It may also be due to any number of other medical conditions, such as infectious mononucleosis, heart problems, or pancreatitis.
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AST/ALT Ratio
While it may seem that a high ALT is all that is needed to diagnose liver disease, its relationship to AST can tell whether the condition isacute(sudden and severe) orchronic(persistent).
For instance, if the liver experiences an acute injury, you can expect a sudden spike in the ALT and a relatively normal (or only mildly elevated) AST.
On the other hand, if liver disease is chronic, the damage will gradually affect other organs. As these organs are damaged, the AST will begin to rise.
The relationship is described with theAST/ALT ratio(also known as theDe Ritis ratio).
The AST/ALT ratio is important because the pattern can tell much about the underlying condition. By way of example:
What Can Affect the Results?
High or low ALT or AST results do not always indicate a health problem. Certain factors can cause a temporary increase or decrease in levels, such as:
Obesity, sex, and age can also influence ALT or AST levels, meaning that what is considered “normal” overall may need to be adjusted if you are overweight or underweight, male or female, or older or younger. Labs will generally take these factors into account.
Summary
8 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.MedlinePlus.Liver function tests.MedlinePlus.Alanine transaminase (ALT) blood test.MedlinePlus.Aspartate aminotransferase (AST) blood test.MedlinePlus.ALT blood test.MedlinePlus.AST test.Oh RC, Hustead TR, Ali SM, Pantsari MW.Mildly elevated liver transaminase levels: causes and evaluation.Am Fam Physician. 2017;96(11):709–15.Newsome P, Cramb R, Davison S, et al.Guidelines on the management of abnormal liver blood tests.Gut.2018;67:6-19. doi:10.1136/gutjnl-2017-314924Stanford Health Care.Liver function tests.
8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.MedlinePlus.Liver function tests.MedlinePlus.Alanine transaminase (ALT) blood test.MedlinePlus.Aspartate aminotransferase (AST) blood test.MedlinePlus.ALT blood test.MedlinePlus.AST test.Oh RC, Hustead TR, Ali SM, Pantsari MW.Mildly elevated liver transaminase levels: causes and evaluation.Am Fam Physician. 2017;96(11):709–15.Newsome P, Cramb R, Davison S, et al.Guidelines on the management of abnormal liver blood tests.Gut.2018;67:6-19. doi:10.1136/gutjnl-2017-314924Stanford Health Care.Liver function tests.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
MedlinePlus.Liver function tests.MedlinePlus.Alanine transaminase (ALT) blood test.MedlinePlus.Aspartate aminotransferase (AST) blood test.MedlinePlus.ALT blood test.MedlinePlus.AST test.Oh RC, Hustead TR, Ali SM, Pantsari MW.Mildly elevated liver transaminase levels: causes and evaluation.Am Fam Physician. 2017;96(11):709–15.Newsome P, Cramb R, Davison S, et al.Guidelines on the management of abnormal liver blood tests.Gut.2018;67:6-19. doi:10.1136/gutjnl-2017-314924Stanford Health Care.Liver function tests.
MedlinePlus.Liver function tests.
MedlinePlus.Alanine transaminase (ALT) blood test.
MedlinePlus.Aspartate aminotransferase (AST) blood test.
MedlinePlus.ALT blood test.
MedlinePlus.AST test.
Oh RC, Hustead TR, Ali SM, Pantsari MW.Mildly elevated liver transaminase levels: causes and evaluation.Am Fam Physician. 2017;96(11):709–15.
Newsome P, Cramb R, Davison S, et al.Guidelines on the management of abnormal liver blood tests.Gut.2018;67:6-19. doi:10.1136/gutjnl-2017-314924
Stanford Health Care.Liver function tests.
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