- The ALT blood test measures alanine aminotransferase, an enzyme that helps detect liver inflammation or injury caused by hepatitis, fatty liver disease, or alcohol use.
- It’s often part of a Comprehensive Metabolic Panel (CMP) and helps monitor liver function, medication effects, or metabolic conditions like diabetes and obesity.
- Elevated ALT levels may indicate liver damage, while persistently high results should be assessed by a doctor through further testing or lifestyle changes.
The AST blood test, also called the aspartate aminotransferase test, measures an enzyme produced mainly by the liver, heart, and muscles. It helps detect liver inflammation or injury and is often ordered with other liver tests like ALT to assess overall liver health.
An AST blood test may be requested when there are signs of liver disease, such as fatigue, yellowing of the skin or eyes, dark urine, or abdominal pain. It can also be part of a routine health check or a Comprehensive Metabolic Panel (CMP) used to monitor how the liver responds to medications or conditions like obesity, diabetes, or viral hepatitis.
Treatment for abnormal AST results depends on the underlying cause and may include lifestyle changes, medication adjustments, or treatment for liver infections. Persistent elevations should be evaluated by a doctor, who may order additional tests like ALT, ALP, or imaging exams to identify possible complications such as fatty liver disease or cirrhosis.
When to do an ALT blood test
The ALT blood test is used to detect liver damage and, so, it can be recommended for people who have a fatty liver or that are overweight. It is also recommended when there are symptoms such as:
- Excessive tiredness;
- Loss of appetite;
- Nausea;
- Vomiting;
- Swelling of the belly;
- Dark urine;
- Yellow skin and eyes.
In the U.S., the ALT or AST blood test is commonly included in the Comprehensive Metabolic Panel (CMP), a routine group of 14 blood tests used to assess liver and kidney function, blood sugar, and electrolytes. Doctors often order it as part of annual checkups or to monitor liver health over time.
This test is also recommended for people at higher risk of metabolic dysfunction-associated steatotic liver disease (MASLD, formerly NAFLD), especially those who are overweight, have diabetes, or consume alcohol frequently.
In addition, the test is used to monitor medications with liver toxicity potential, such as statins, antiepileptics, antituberculosis drugs, and antivirals for hepatitis B or C. Regular ALT and AST monitoring helps detect early liver injury and guide treatment decisions.
Normal range results
Most U.S. laboratories consider normal levels to be 7 to 55 U/L for men and 7 to 45 U/L for women.
In the United States, normal ALT values vary slightly depending on the laboratory.
High ALT levels
High ALT levels are typically characterized by how elevated they are compared to the base line level.
- 4x higher than normal: is normally a sign of chronic hepatitis caused by cirrhosis or cancer.
- 10x higher than normal: is usually a change caused by acute hepatitis due to viruses or the use of drugs;
- 100x higher than normal: is very common in people who use drugs, alcohol or other substances that cause severe liver damage.
Despite being a very specific marker for liver damage, ALT can also be found in muscles and in the heart tissue. Therefore an increase in the concentration of this enzyme can also be seen after intense physical exercise.
To assess liver function and identify any damage, the doctor may also request other types of blood test to check for other enzymes, such as lactate dehydrogenase (LDH) and AST (or SGOT).
Learn more about ALT and AST testing, and why they are often interpreted together.
What to do for high ALT levels
When ALT levels are consistently high, your doctor may refer you to a specialist for more thorough assessment of your clinical history to identify what may be causing damage to the liver. The specialist may order more specific testing, such as hepatitis tests or a liver biopsy, to confirm a diagnosis.
Furthermore, in cases of high ALT, it is also recommended to follow an adequate diet for the liver, which should be low in fats and giving preference to boiled foods. Learn more about what foods you should eat and avoid when trying to heal your liver.
Low ALT levels
Low ALT levels on their own is usually not clinically significant, especially if the patient does not present with signs or symptoms.
However, it may associated with a health condition like a UTI, liver cancer or azotemia (a condition that is characterized by increased urea and creatinine in the blood). Therefore low ALT levels that present with other symptoms should be investigated with further testing.