AST (aspartate aminotransferase)

DESCRIPTION: AST catalyzes a reversible transamination reaction between L-spartate and alpha-oxoglutarate. Pyridoxal-5-phosphate (P-5-P) is the prosthetic group of AST. The enzyme is localized in the cytoplasm and mitochondria of liver, heart muscle and skeletal muscle cells. The catalytic concentration of AST is measured in the serum of patients with heart and liver damage. DETERMINATION: Sample: Serum, plasma (heparin). Sample stability is 4 days if stored at 20-25°C, 7 days at 2°C to 8°C, 12 weeks at -20°C Measurement units: U/L Recommended method and/or procedure I: UV method (IFCC) AST catalyzes the transfer of amino groups from aspartate to alpha-ketoglutarate, resulting in glutamate and oxaloacetate. In the indicator reaction, oxaloacetate is reduced to malate under the influence of malate dehydrogenase, with the simultaneous oxidation of an equivalent amount of NADH to NAD+. The result is a decrease in absorbance, which is measured spectrophotometrically, and which is directly proportional to the catalytic activity of AST in the serum. LDH is added to quickly reduce any pyruvate present in the serum and thus eliminate its interference during the test. CLINICAL SIGNIFICANCE: 1) Physiological changes in the catalytic concentration of AST AST is increased in normal newborns. The level as in adults is reached by 7 years of age 2) Pathological changes in the catalytic concentration of AST A) Increased values of the catalytic concentration of AST in: Heart diseases: In myocardial infarction, AST can increase 4-10 times compared to reference values. AST values in the serum begin to rise after 3 hours, and reach the highest values after 24 hours (4-10 times), and return to normal again after 3-4 days. AST is not specific enough to detect small infarcts. In these cases, it is better to determine CK, LDH or HBDH. AST can also be increased in patients with acute cardiac congestive decompensation, arrhythmia or severe angina. Acute rheumatic heart inflammation – values depend on the severity of the disease. On the second day after heart surgery, AST values increase (7-8 times higher than normal), and after 10 days they return to normal. After external heart massage and after angiocardiography and heart catheterization. Liver diseases: In liver diseases, AST values can be 10-100 times higher than normal: Alcoholics / Lung infarction / AST rises more slowly and reaches maximum values later than in myocardial infarction / Infectious mononucleosis (highest values in the second week of the disease, and return to normal in the 5th week) / Infiltration of the liver (AST can be increased) / Cancer / In therapy or poisoning with salicylates / The increase in AST is proportional to the values salicylate in plasma [conc. salicalata >1.81 mmol/L (25 mg/L)] / Cholangitis / Leukemia / Lymphoma / Carbon tetrachloride liver damage / Rimpampicin and isoniazid therapy / Infectious jaundice Pancreatic diseases: Acute pancreatitis / Rise of AST only if serum bilirubin is increased (biliary obstruction) Trauma: “Crush” syndrome / Intestinal infarction / Severe heatstroke / Local radiation injury / After direct current defibrillation / After intramuscular injection of ampicillin or carbenicillin / CO2 and CO poisoning (AST from muscle, heart and brain) / Hornet sting Other diseases: Acute hemolytic anemia / Acute kidney disease / Dermatomyositis / Gout (in the acute phase) / Myoglobinuria / At the beginning of clofibrate treatment / Progressive muscular dystrophy / Status asthmaticus / Severe burns B) Decreased values of the catalytic concentration of AST in: Beriberi / Uncontrolled diabetes mellitus with acidosis RISK FACTORS: Decreased values: – A slight decrease was observed during pregnancy when there is an abnormal metabolism of pyridoxine – Oxalates – Salicylates can be the cause of falsely decreased AST values – High catalytic concentration of GLDH in the serum Elevated values: – Alcoholism – Hemodialysis patients (pyruvate, pyridoxal phosphate) – Starvation (1.5 g/L) – Hemolyzed serum samples contain up to 10 times more AST than in normal serum – During therapy or salicylate poisoning – Vascular ligation >1 minute (9.3% increase) – Body position: lying down – standing (5% increase) – Salicylates can be the cause of falsely increased AST values EFFECT OF DRUGS: Decreased values: acetaminophen, aminophenazone, ascorbic acid, clothiapine, dipyrone, fluosol, ibuprofen, ketoprofen, metronidase, pindolol, rifampin Increased values: acetaminophen, aminosalicylic acid, ascorbic acid (conc. > 1 mmol/L), diclofenac, erythromycin, phenelzine, fluorides, gentamicin, isoniazid, isoproterenol, levodopa, methyldopa (conc. > 1 mmol/L), nitrofurantoin, pyridoxal, sulfathiazole, tolbutamide RESULT: The reference interval depends on age, gender and work method. The reference interval is displayed on each validated result.