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Introduction ⬇

AST is an enzyme present in tissues of high metabolic activity; decreasing concentrations of AST are found in the heart, liver, skeletal muscle, kidney, brain, pancreas, spleen, and lungs. The enzyme is released into the circulation following the injury or death of cells. Any disease that causes change in these highly metabolic tissues will result in a rise in AST levels. The amount of AST in the blood is directly related to the number of damaged cells and the amount of time that passes between injury to the tissue and the test. Following severe cell damage, the blood AST level will rise in 12 hours and remain elevated for about 5 days.

This test is used to evaluate liver and heart disease. ALT is usually ordered along with the AST.

Normal Findings ⬆ ⬇

Men: 14–20 U/L or 0.23–0.33 μkat/L

Women: 10–36 U/L or 0.17–0.60 μkat/L

Newborns: 47–150 U/L or 0.78–2.5 μkat/L

Children: 9–80 U/L or 0.15–1.3 μkat/L

Normal values vary widely according to method of testing; check with your laboratory for reference values.

Clinical Alert

Critical ValueAST is extremely high (>20,000 U/L; >333 kat/L) in alcohol–acetaminophen syndrome.AST > ALT, prothrombin time: 100 secondsCreatinine: >34 mg/L or >0.30 mmol/L

Procedure ⬆ ⬇

  1. Obtain a 5-mL venous sample (red-topped tube). Serum is used. Observe standard precautions. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered. Place the specimen in a biohazard bag.

  2. Avoid hemolysis.

Clinical Implications ⬆ ⬇

  1. Increased AST levels occur with MI.

    1. With MI, the AST level may be increased to 4–10 times the normal values.

    2. The AST level reaches a peak in 24 hours and returns to normal by post-MI days 3–7. Secondary rises in AST levels suggest extension or recurrence of MI.

    3. The AST curve in MI parallels that of creatine phosphokinase (CPK).

  2. Increased AST levels occur in liver diseases (10–100 times normal).

    1. Acute hepatitis and chronic hepatitis (ALT > AST)

    2. Active cirrhosis (drug induced; alcohol induced: AST > ALT)

    3. Infectious mononucleosis

    4. Hepatic necrosis and metastasis

    5. Primary or metastatic carcinoma

    6. Alcoholic hepatitis

    7. Reye syndrome

  3. Other diseases associate with elevated AST levels include the following:

    1. Hypothyroidism

    2. Trauma and irradiation of skeletal muscle

    3. Dermatomyositis

    4. Polymyositis

    5. Toxic shock syndrome

    6. Cardiac catheterization

    7. Recent brain trauma with brain necrosis, cerebral infarction

    8. Crushing and traumatic injuries, head trauma, surgery

    9. Progressive muscular dystrophy (Duchenne)

    10. Pulmonary emboli, lung infarction

    11. Gangrene

    12. Malignant hyperthermia, heat angiography

    13. Mushroom poisoning

    14. Shock

    15. Hemolytic anemia, exhaustion, heat stroke

  4. Decreased AST levels occur in the following conditions:

    1. Azotemia

    2. Chronic kidney dialysis

    3. Vitamin B6 deficiency

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purpose and blood-drawing procedure.

  2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Monitor appropriately for heart and liver diseases.

  2. Ensure that unexplained AST elevations are further investigated with ALT and GGT tests.

  3. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

  1. Slight decreases occur during pregnancy when there is abnormal metabolism of pyridoxine.

  2. Many drugs can cause elevated or decreased levels (see Appendix E). Alcohol ingestion affects results.

  3. Exercise and IM injections do not affect results.

  4. False decreases occur in diabetic ketoacidosis, severe liver disease, and uremia.

  5. Gross hemolysis causes falsely high levels.