Also Known As
Serum Glutamic-Pyruvic Transaminase
Alanine Transaminase
This article was last reviewed on
This article waslast modified on December 4, 2020.
At a Glance
Why Get Tested?

To screen for liver damage and/or to help diagnose liver disease

When To Get Tested?

When a healthcare practitioner thinks that you have symptoms of a liver disorder, such as abdominal pain, nausea and vomiting, jaundice (yellowish discoloration of the skin or white of the sclerae), or potential exposure to hepatitis viruses; it can also be ordered as part of a comprehensive metabolic panel (CMP) when you have a routine health exam.

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?


You may be able to find your test results on your laboratory's website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab's website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab's website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called "normal" values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."

For more information, please read the article Reference Ranges and What They Mean.

What is being tested?

Alanine aminotransferase (ALT) is an enzyme found mostly in the cells of the liver and kidney. Much smaller amounts of it are also found in the heart and muscles. Normally, ALT levels in blood are low, but when the liver is damaged, ALT is released into the blood and the level increases. This test measures the level of ALT in the blood and is useful for early detection of liver disease.

The function of ALT is to convert alanine, an amino acid found in proteins, into pyruvate, an important intermediate in cellular energy production. In healthy individuals, ALT levels in the blood are low. When the liver is damaged, ALT is released into the blood, usually before more obvious signs of liver damage occur, such as jaundice.

The liver is a vital organ located in the upper right side of the abdomen, just beneath the rib cage. It is involved in many important functions in the body. The liver helps to process the body's nutrients, manufactures bile to help digest fats, produces many important proteins such as blood clotting factors and albumin, and breaks down potentially toxic substances into harmless ones that the body can use or eliminate.

A number of conditions can cause damage to liver cells, resulting in an increase in ALT. The test is most useful in detecting damage due to hepatitis (inflammation of the liver) or as a result of drugs or other substances that are toxic to the liver.

ALT is commonly tested in conjunction with aspartate aminotransferase (AST), another liver enzyme, as part of a liver panel. Both ALT and AST levels usually rise whenever the liver is being damaged, although ALT is more specific for the liver and, in some cases, may be the only one of the two to be increased. An AST/ALT ratio may be calculated to aid in distinguishing between different causes and severity of liver injury and to help distinguish liver injury from damage to heart or muscles.

Accordion Title
Common Questions
  • How is the test used?

    The alanine aminotransferase (ALT) test is typically used to detect liver injury. It is often ordered in conjunction with aspartate aminotransferase (AST) as part of a liver panel or comprehensive metabolic panel (CMP) to screen for and/or help diagnose liver disease.

    AST and ALT are considered to be two of the most important tests to detect liver injury, although ALT is more specific to the liver than is AST. Sometimes AST is compared directly to ALT and an AST/ALT ratio is calculated. This ratio may be used to distinguish between different causes of liver damage and to help recognize heart or muscle injury.

    ALT values are often compared to the results of other tests such as alkaline phosphatase (ALP), gamma glutamyl transferase (GGT), total protein, albumin-to-globulin ratio (A/G ratio), and bilirubin to help determine which form of liver disease is present.

    ALT is often used to monitor the treatment of liver disease, to see if the treatment is working, and may be ordered either by itself or along with other tests for this purpose.

  • When is it ordered?

    ALT may be ordered as part of a comprehensive metabolic panel when you have a routine health examination.

    A healthcare practitioner usually orders an ALT test (and several others) when you have signs and symptoms of a liver disorder. Some of these signs and symptoms may include:

    • Weakness, fatigue
    • Loss of appetite
    • Nausea, vomiting
    • Abdominal distension/fullness and/or pain
    • Jaundice (icterus)
    • Dark urine or tea-colored urine 
    • Light-colored stool or clay-colored stool
    • Skin itchiness (pruritus)

    ALT may also be ordered, either by itself or with other tests, when you have an increased risk for liver disease. This is because many people with mild liver damage will have no signs or symptoms. Even without symptoms, ALT can be increased with mild liver damage. You may be at risk of liver disease when you:

    ALT may be ordered on a regular basis when it is used to monitor the treatment of liver disease.

  • What does the test result mean?

    A low level of ALT in the blood is expected and is normal. Liver disease is the most common reason for higher than normal levels of ALT.

    Very high levels of ALT (more than 10 times normal) are usually due to acute hepatitis, sometimes due to a viral hepatitis infection. In acute hepatitis, ALT levels usually stay high for about 1-2 months but can take as long as 3-6 months to return to normal. Levels of ALT may also be markedly elevated (sometimes over 100 times normal) as a result of exposure to drugs or other substances that are toxic to the liver or in conditions that cause decreased blood flow to the liver.

    ALT levels are usually not much elevated in chronic hepatitis, often less than 4 times normal. In this case, ALT levels often vary between normal and slightly increased, so the test may be ordered frequently to see if there is a pattern. Other causes of moderate increases in ALT include obstruction of bile ducts, cirrhosis (usually the result of chronic hepatitis or bile duct obstruction), heart damage, alcohol abuse, and with tumors in the liver.

    ALT is often performed together with a test for AST or as part of a liver panel. For more about ALT results in relation to other liver tests, see the Liver Panel article.

    In certain types of liver diseases, the ALT level is higher than AST and the AST/ALT ratio will be low (less than 1). There are a few exceptions; the AST/ALT ratio is usually greater than 1 in alcoholic hepatitis, cirrhosis, and with heart or muscle injury and may be greater than 1 for a day or two after onset of acute hepatitis.

  • Is there anything else I should know?

    A shot or injection of medicine into the muscle tissue, or strenuous exercise, may increase ALT levels.

    Many drugs may raise ALT levels by causing liver damage in a very small percentage of patients taking the drug. This is true of both prescription drugs and some "natural" health products. Be sure to tell your healthcare provider about all of the drugs and/or health supplements you are taking.

  • What conditions other than liver problems can cause increased ALT?

    ALT is more specific for the liver than AST and so is much less affected by conditions affecting other parts of the body. Nevertheless, injury to organs other than the liver, such as the heart and skeletal muscle, can cause elevations of ALT. For example, small increases may be seen with skeletal muscle damage or heart attacks.

  • What other tests may be performed to help determine the cause of liver damage?

    After a thorough physical exam and evaluation of a person's medical history, there are several other tests that may be performed as follow up depending on what is suspected to be the cause of liver damage. Some of these include:

    A liver biopsy may be performed to help determine the cause of liver injury and to evaluate the extent of liver damage.

    For more information, see the article on Liver Disease.

Health Professionals – LOINC

Logo for LOINC from RegenstriefLOINC Observation Identifiers Names and Codes (LOINC®) is the international standard for identifying health measurements, observations, and documents. It provides a common language to unambiguously identify things you can measure or observe that enables the exchange and aggregation of clinical results for care delivery, outcomes management, and research. Learn More.

Listed in the table below are the LOINC with links to the LOINC detail pages. Please note when you click on the hyperlinked code, you are leaving Lab Tests Online and accessing

LOINC LOINC Display Name
77144-4 ALT (S/P/Bld) [Catalytic activity/Vol]
1742-6 ALT [Catalytic activity/Vol]
1744-2 ALT No additional P-5'-P [Catalytic activity/Vol]
1743-4 ALT With P-5'-P [Catalytic activity/Vol]
44785-4 ALT No additional P-5'-P (Stdy maximum) [Catalytic activity/Vol]
76625-3 ALT (Bld) [Catalytic activity/Vol]
16324-6 ALT (RBC) [Catalytic activity/Vol]
1916-6 AST/Alanine aminotransferase [Catalytic ratio]
96586-3 ALT (DBS) [Catalytic activity/Vol]
View Sources

Sources Used in Current Review

2019 Review completed by H.L.Chong, MD, FRSPH, IPFPH, Clinical Scholar, Faculty of Public Health of the Royal Society of Physicians of United Kingdom.

ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries. The American Journal of Gastroenterology. Volume 112. January 2017.

(Updated June 13, 2019) Sood, G MD. Acute Liver Failure Workup. Medscape Reference. Available online at Accessed August 2019.

McPherson RA, Matthew R, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia: Elsevier Saunders; 2011.

Sources Used in Previous Reviews

Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. St. Louis: Mosby; 1998.

Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER and Bruns DE, eds. 4th ed. St. Louis, Missouri: Elsevier Saunders; 2006, Pp 604-606.

Kasper DL, Braunwald E, Fauci AS, Hauser SL, Longo DL, Jameson JL eds, (2005) Harrison's Principles of Internal Medicine, 16th Edition, McGraw Hill, Pp 1811-1815.

Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. 3rd Edition, St. Louis: Mosby Elsevier; 2006, Pp 40-42.

Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC, Pp 270-271.

Carey, W (January 1, 2009) Approach to the Patient with Liver Disease: A Guide to Commonly Used Liver Tests, Cleveland Clinic. Available online at Accessed February 2010.

Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson RA and Pincus MR, eds. Philadelphia: 2007, Pp 268-269.

(2000) Dufour, DR et al. National Academy of Clinical Biochemistry Standards of Laboratory Practice: Laboratory Guidelines for Screening, Diagnosis and Monitoring of Hepatic Injury Accessed February 2010.

(March 15, 2005) Giboney, P. Mildly Elevated Liver Transaminases in the Asymptomatic Patient. Am Fam Physician 2005; 71:1105–10. Available online at Accessed February 2010.

(Feb 22, 2009) MedlinePlus Medical Encyclopedia: ALT. Available online at Accessed February 2010.

Alanine Aminotransferase (ALT) (GPT), Serum. Mayo Clinic. Available online at Accessed September 2013.

Orlewicz, M. S. (Update April 20, 2012.) Alanine Aminotransferase. Medscape. Available online at Accessed September 2013.

Nyblom, H. et. al. (July 2004.) High AST/ALT Ratio May Indicated Advanced Alcoholic Liver Disease Rather Than Heavy Drinking. National Center for Biotechnology Information PubMed. Available online at Accessed September 2013.

2016 review performed by Alan F. Weir, PhD, DABCC, Instructor, Fox Valley Technical College.

(September 9, 2014) Thompson, E. Gregory, MD. Alanine Aminotransferase (ALT). WebMD. Available online at Accessed on 4/05/16.

(September 5, 2014) Orlewicz, Marc S, MD. Alanine Aminotransferase. Medscape. Available online at Accessed on 4/05/16.

(June 2014) Durani, Yamini, MD. Blood Test: Alanine Aminotransferase (ALT, or SGPT). KidsHealth from Nemours. Available online at Accessed on 4/05/16.

(April 30, 2015) Davis, Charles Patrick, MD, PhD. Liver Blood Tests. MedicineNet. Available online at Accessed on 4/05/16.

(December 30, 2014) Ratini, Melinda, DO, MS. Liver Function Tests. WebMD. Available online at Accessed on 4/07/16.

Alanine aminotransferase. Nursing Central, Davis's Lab and Diagnostic Tests. Available online at Accessed on 4/05/16.

Alanine Aminotransferase. MedFriendly. Available online at Accessed on 4/05/16.

Giboney, Paul T., MD. Mildly Elevated Liver Transaminase Levels in the Asymptomatic Patient. Am Fam Physician. 2005 Mar 15;71(6):1105-1110. Available online at Accessed on 4/05/16.

(December 21, 2015) Blocka, Carla. ALT (Alanine Aminotransferase) Test. Healthline. Available online at Accessed on 4/05/16.

Test ID: ALT Alanine Aminotransferase (ALT) (GPT), Serum. Mayo Clinic, Mayo Medical Laboratories. Available online at Accessed on 4/05/16.

(February 8, 2015) Martin, Laura J., MD, MPH. Alanine transaminase (ALT) Blood test. US National Library of Medicine, MedlinePlus. Available online at Accessed on 4/05/16.

McPherson, Richard A., MD. & Pincus, Matthew R., MD, PhD. (© 2007). Henry's Clinical Diagnosis and Management by Laboratory Methods 21st Edition: Saunders, Philadelphia, PA. Pp. 22, 263, 268-269.

Burtis, Carl A., Ashwood, Edward R., & Bruns, David E. (© 2007). Tietz Fundamentals of Clinical Chemistry 6th Edition: Saunders, Philadelphia, PA. Pp 318-319, 322-324, 686-688.

Fischbach, Francis. (© 2000). A Manual of Laboratory and Diagnostic Tests 6th Edition: Lippincott, Philadelphia, PA. Pp 428-430.

LeFever, Joyce. (© 1999). Kee Laboratory and Diagnostic Tests with Nursing Implications 5th Edition: Appleton and Lange, Stanford, CT. Pp 15-17.

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