Alanine Aminotransferase (ALT, GPT)

Alanine aminotransferase (ALT, ALAT; also called glutamate pyruvate transaminase (GPT)) is an enzyme produced in liver cells. ALT is a marker of inflammatory (“inflammatory”) damage to the liver parenchyma (part of the liver that contains hepatocytes). Alanine aminotransferase, like aspartate aminotransferase (AST, ASAT; also called glutamate oxaloacetate transaminase (GOT)), belongs to the transaminases. These are enzymes that catalyze the transfer of α-amino groups from a donor to an acceptor molecule (transamination). ALT (GPT) is liver-specific. It has an approximately 10-fold higher specific activity in the liver than in the myocardium (heart muscle) and skeletal muscle and is mainly present dissolved in the cytoplasm (basic structure filling the cell). ALT is thus suitable as a search enzyme for liver disease and is of differential diagnostic importance only in muscle disease and in myocardial infarction (heart attack).

The procedure

Material needed

  • Blood serum

Preparation of the patient

  • Not necessary

Disruptive factors

  • Avoid hemolysis! This leads to highly pathological elevation of ALT (ALT is 7-fold higher in erythrocytes (red blood cells) than in the serum!)
  • Strong muscle work
  • Supplements containing red rice or green tea may cause abnormal changes in liver enzymes.
  • Medications (see under “Hepatotoxic Medications”).

Normal values

Gender Normal values in U/l according to old reference range (measurement 25 °C) Normal values in U/l according to new reference range (measurement 37 °C)
Female < 19 10-35
Male < 23 10-50
Newborn, 1st month of life 4-32 –
2nd-12th month of life 6-36 –
> 1. year of life 5-21 –

Indications

  • Diagnosis, differentiation and follow-up of liver and biliary tract diseases.

Interpretation

Interpretation of increased values

  • Alcohol dependence [AST > ALT]
  • Acute circulatory disorder
  • Acute hepatitis (liver inflammation) (high levels) [ALT > AST]
  • Alpha-1 antitrypsin deficiency [ALT > AST]
  • Autoimmune hepatitis (AIH; autoimmune hepatitis) (esp. women) [ALT > AST]
  • Cholangitis (biliary tract inflammation).
  • Cholestasis (bile stasis)
  • Cholecystitis (gallbladder inflammation)
  • Chronic hepatitis (inflammation of the liver)
  • Genetic diseases* such as muscular dystrophy, cystic fibrosis (cystic fibrosis) progressive muscular dystrophy, celiac disease (gluten-induced enteropathy; chronic disease of the mucosa of the small intestine (small intestinal mucosa) due to hypersensitivity to the cereal protein gluten).
  • Hemochromatosis (iron storage disease) [ALT> AST]
  • Infections (after foreign travel)
  • Liver metastases
  • Liver tumors (low elevated levels)
  • Liver cirrhosis – connective tissue remodeling of the liver with resulting functional impairment.
  • Pulmonary embolism – occlusion of blood vessels supplying the lungs by an embolus (blood clot).
  • Mononucleosis (Pfeiffer’s glandular fever) – infectious disease caused by the Epstein-Barr virus (EBV).
  • Wilson’s disease (copper storage disease) [ALT > AST]
  • Muscle diseases such as myositis (muscle inflammation).
  • Myocardial infarction (heart attack) [ALT only significant in the course if right heart failure (right heart weakness) is suspected in myocardial infarction]
  • Myocarditis (inflammation of the heart muscle).
  • Primary biliary cholangitis/biliary duct inflammation (PBC, synonyms: nonpurulent destructive cholangitis; formerly primary biliary cirrhosis) – relatively rare autoimmune disease of the liver (affects women in about 90% of cases); detection of antimitochondrial antibody (AMA).
  • Steatosis hepatis (fatty liver) [non-alcoholic fatty liver: ALT > AST]
  • Trauma (injuries)
  • Toxic/drug-induced liver injury (see “Hepatotoxic drugs” below.
  • Celiac disease (in 5-10% of cases).

* Ca. 12% of isolated aminotransferases elevation of a pediatric clinic.

Interpretation of decreased values

  • Not relevant to disease
  • ALT level < 17 U/l: patients with stable coronary artery disease (CAD) increase in mortality (death rate) by 11% (hazard ratio 1.11; 95% confidence interval 1.03-1.19; p < 0.01)

Additional notes

  • ALT (GPT) is serologically detectable at low levels of liver injury due to its cytoplasmic localization in hepatocytes.
  • Intraindividual variation in aminotransferases is approximately 10-30% from day to day; elevated activities can also be measured during vigorous exercise.
  • In the population-based SHIP study in Mecklenburg-Vorpommern, abnormally elevated ALT activity was found in 24.6% of the individuals studied.
  • De-ritis quotient (= AST/ALT) allows conclusions about the severity of hepatocyte damage in liver disease:
    • acute hepatitis:
      • <1: uncomplicated course
      • > 1: complicated course
      • – 2: alcoholic hepatitis
    • chronic hepatitis:
      • < 1 (frequent); elevated ALT (GPT) levels > 6 months → chronic hepatitis.
    • Liver cirrhosis:
    • Non-hepatic (trauma/myocardial infarction): > 1
  • Approximately 15% of patients with liver and biliary tract disease (extrahepatic bile duct obstruction, liver metastases, cirrhosis, drug-induced liver injury) do not show ALT elevation.
  • ALT (GPT) is mainly present dissolved in the cytoplasm (85%), but is also bound in mitochondria (15%):
    • Mild liver damage → membrane-bound gamma-GT ↑
    • Moderate liver damage → cytoplasmic ALT (GPT) ↑ and AST (GOT) ↑
    • Severe liver damage → mitochondrial GLDH ↑ and AST (GOT) ↑
  • The half-life is 47 h.

Further diagnostics

  • To determine liver function, aspartate aminotransferase (AST, GOT), glutamate dehydrogenase (GLDH), gamma-glutamyl transferase (gamma-GT), alkaline phosphatase (AP) and bilirubin should also always be measured. If necessary, also albumin (liver synthesis) and blood countBy the simultaneous determination of AST, ALT and γ-GT can be detected more than 95% of all liver diseases.To the basal clarification is also mandatory a liver sonography!
  • Further diagnostics for elevated liver values is indicated if:
    • Chronic (> 6 months) existing
    • Symptomatic
    • Exceeding three times the norm
  • Basal workup for elevated liver enzymes – the most common causes are nonalcoholic fatty liver disease (NAFLD) or alcohol abuse – includes mandatory liver sonography and screening for chronic hepatitis B and C!