-Glutamyl transpeptidase (GGT), an isoenzyme of ALP, catalyzes the transfer of glutamyl groups among peptides and amino acids. Hepatobiliary tissues and renal tubular and pancreatic epithelia contain large amounts of GGT. Other sources include the prostate gland, brain, and heart.

Most GGT in serum derives from hepatobiliary sources, and elevated levels point to hepatobiliary disease.

• Alcohol, barbiturates, and phenytoin may elevate GGT levels.
• Late pregnancy and oral contraceptives may produce lower than normal values.

• Elevated alkaline phosphatase of uncertain etiology:
  • Pronounced elevations are seen in clients with obstructive disorders of the hepatobiliary tract and hepatocellular carcinoma.
  • Modest elevations occur with hepatocellular degeneration (e.g., cirrhosis) and with pancreatic or renal cell damage or neoplasms.
  • Other disorders associated with elevated GGT levels include CHF, acute myocardial infarction (after 4 to 10 days), hyperlipoproteinemia (type IV), diabetes mellitus with hypertension, and epilepsy.
  • Normal levels in the presence of elevated ALP support the diagnosis of bone disease.
• Known or suspected alcohol abuse, including monitoring of individuals participating in alcohol abstinence programs
  • About 60 to 80 percent of individuals considered to have alcohol abuse problems have elevated GGT levels, whether or not other signs of liver damage are present.
  • Moderate increases in GGT levels occur with low alcohol intake.
  • A significant sustained rise occurs with ingestion of six or more drinks per day.
  • Normal levels return within 2 to 6 weeks of abstinence from alcohol.

Nursing Care Before the Procedure

Client preparation is essentially the same as that for any test involving collection of a peripheral blood sample (see Appendix I).

• Some laboratories require the client to fast from food for 8 hours before the test.
• When the test is conducted to determine whether the liver is the source of elevated ALP, the client should abstain from alcohol for 2 to 3 weeks before the test. This restriction may not apply when the test is used to monitor compliance with alcohol abstinence programs.
• The client's reported intake (or nonintake) of alcohol should, however, be noted.

A venipuncture is performed and the sample 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 food withheld before the test.