Aspartate aminotransferase (AST), formerly known as glutamic-oxaloacetic transaminase (GOT), catalyzes the reversible transfer of an amino between the amino acid, aspartate, and -ketoglutamic acid. ALT exists in large amounts in both liver and myocardial cells and in smaller but significant amounts in skeletal muscles, kidneys, pancreas, and brain.

Serum AST rises when cellular damage occurs to the tissues in which the enzyme is found. When heart muscle suffers ischemic damage, serum AST rises within 6 to 8 hours; peak values occur at 24 to 48 hours and decline to normal within 72 to 96 hours. Elevation of AST occurs midway in the time sequence between that of creatine phosphokinase (CPK), which rises very early and falls within 48 hours, and lactic dehydrogenase, which begins rising 12 hours or more after infarction and remains elevated for a week or more. Elevation of AST cannot be used as the single enzyme indicator for myocardial infarction, because it also rises in several other conditions included in the differential diagnosis of heart attack. Other disorders associated with elevated AST, and the magnitude of those elevations, are listed in Table 5-17. Note also that numerous drugs, especially those known to be hepatotoxic or nephrotoxic, may elevate AST levels.²⁷

The test for AST was formerly known as serum glutamic-oxaloacetic transaminase (SGOT).

• Numerous drugs may falsely elevate levels.

• Suspected disorders or injuries involving the liver, myocardium, kidneys, pancreas, or brain, with elevated levels indicating cellular damage to tissues in which AST is normally found (see Table 5-17):
  • In myocardial infarction, AST rises within 6 to 8 hours, peaks at 24 to 48 hours, and declines to normal within 72 to 96 hours.
• Monitoring of response to therapy with potentially hepatotoxic or nephrotoxic drugs
• Monitoring of response to treatment for various disorders in which AST may be elevated, with tissue repair indicated by declining levels

Nursing Care Before the Procedure

General client preparation is the same as that for any study involving collection of a peripheral blood sample (see Appendix I).

• Because many drugs alter AST levels, a medication history should be obtained. It is recommended that any drugs that may alter test results be withheld for 12 hours before the test, although this practice should be confirmed with the person ordering the study.

A venipuncture is performed and the sample is collected in a red-topped tube. The sample should be handled gently to avoid hemolysis and transported promptly to the laboratory.

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving the collection of a peripheral blood sample.

• Resume any drugs withheld before the test, pending test results.
• Complications and precautions: Increases in this enzyme level in relation to ALT and other assessment data may indicate a cardiac disorder. Monitor vital signs and cardiac activity by electrocardiogram (ECG).