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Lab Test: Alanine Aminotransferase (ALT)

    Lab Test

    Alanine Aminotransferase (ALT)

    • Synonyms:  Formerly Serum Glutamic-Pyruvic Transaminase [SGPT]), Glutamic pyruvate transaminase measurement

    Alanine aminotransferase (ALT) is an enzyme found primarily in the cytosol of liver cells and is commonly evaluated along with the AST (aspartate aminotransferase).  As suggested by their names "aminotransferase", these intracellular enzymes are involved in the modification of amino acids in the liver. When the liver undergoes an injury or damage these enzymes are released into the blood, but ALT is more specific to the liver.  In patients presenting with jaundice, an abnormal alanine aminotransferase (ALT) will incriminate the liver rather than red blood cell (RBC) hemolysis as a source of the jaundice.

    Reference Range

    • Adult/child:  4-36 international units/L at 37° C or 4-36 units/l (SI units);
    • PDR:  Adults:  0-35 units/L (0-0.58 microkat/L)
    • Values may be higher in men and in African Americans
    • Infant:  may be twice as high as adult values
    •  Elderly:  may be slightly higher than adult values
    Indications & Uses
    • Evaluation of liver enzymes prior to starting certain medications (e.g., isoniazide, statins, terbinafine)
    • Most ALT elevations are caused by liver dysfunction.  Therefore, this enzyme is not only sensitive but also quite specific for hepatocellular disease. 
    • In hepatocellular disease other than viral hepatitis the ALT:AST (aspartate aminotransferase) ratio (DeRitis ratio) is less than 1.  In viral hepatitis the ratio is greater than 1.  This is helpful in the diagnosis of viral hepatitis. 
    • Evaluation of hepatic steatosis or non-alcoholic fatty liver disease (NALD) in patients who commonly have diabetes mellitus, suffer from obesity or hyperlipidemia. 
    • Evaluation of patients with Wilson's disease
    Clinical Application

    Significantly increased levels:

    • Hepatitis (traditional normal range cut-off value is 40 IU/L)
    • Hepatic necrosis
    • Hepatic ischemia
    • Viral hepatitis (Peak ALT levels vary from 400 to 4000 IU or more in acute hepatitis)
    • Acute hepatitis C (serum ALT levels are more than 7 times the upper limit of normal)

    Moderately increased levels:

    • Cirrhosis, cholestasis
    • Cholecystitis (ALT values elevated in 40% to 75% of cases, usually to less than 5 times normal) Ehrlichiosis
    • Hepatic steatosis
    • Hepatic tumor
    • Hepatotoxic drugs
    • Obstructive jaundice
    • Severe burns
    • Trauma to striated muscle

    Mildly increased levels:

    • Myositis
    • Pancreatitis
    • Myocardial infarction
    • Infectious mononucleosis
    • Shock or hypotension (injury or disease affecting the liver, heart, or skeletal muscles will cause a release of this enzyme into the bloodstream, thus elevating serum ALT levels.)
    • Exercise or strenuous physical activity prior to the lab draw
    • Hemolysis of the blood sample at time of venipuncture
    Related Tests
    • Acetaminophen (Tylenol) Level
    • Aspartate aminotransferase (AST)
    • Bilirubin Levels
    • Ethanol (Alcohol) Level
    • Gamma-glutamyl transpeptidase (GGTP)
    • Alkaline phosphatase
    • 5'-nucleotidase
    • Creatine kinase (CK)
    • Lactic dehydrogenase (LDH)
    • Leucine aminopeptidase
    Drug-Lab Interactions
    • Previous intramuscular (IM) injections may sometimes cause elevated levels
    • Drugs that may cause increased ALT levels can include:  acetaminophen (usually in high doses), allopurinol, aminosalicylic acid, ampicillin, azathioprine, carbamazepine, cephalosporins, chlordiazepoxide, chlorpropamide, clofibrate, cloxacillin, codeine, dicumarol, HMG CoA Reductase inhibitors (i.e., statins), indomethacin, isoniazid (INH), methotrexate, methyldopa, nafcillin, nalidixic acid, nitrofurantoin, oral contraceptives, oxacillin, phenothiazines, phenylbutazone, phenytoin, procainamide, propoxyphene, propranolol, quinidine, salicylates, statins, terbinafine, tetracyclines, and verapamil.
    Test Tube Needed
    • Collect 7 mL blood in red-top tube
    • Collect a venous blood sample and send it to the laboratory for analysis. 
    • Apply pressure or a pressure dressing to the venipuncture site and assess the site for bleeding.  Patients with liver dysfunction often have prolonged clotting times and have a greater risk of bleeding.
    Storage and Handling
    • Analyze specimen within 12 to 24 hours after collection
    What To Tell Patient Before & After
    • Explain the procedure to the patient and tell them that no fasting is required.
    • Green RM et al.  American Gastroenterological Association.  AGA Technical Review on the Evaluation of Liver Chemistry Tests.  Gastroenterology  2002;123(4):1367-84.  PMID: 12360498
    • LaGow B et al., eds. PDR Lab Advisor. A Comprehensive Point-of-Care Guide for Over 600 Lab Tests.  First ed. Montvale, NJ: Thomson PDR; 2007.
    • Pagana K, Pagana TJ eds. Mosby's Manual of Diagnostic and Laboratory Tests. 5th Ed.  St. Louis, Missouri. 2014.

MESH Terms & Keywords

  • ALT, Alanine Aminotransferase, ALT Lab Test, ALT Liver Enzymes