γ-Glutamyl Transferase (GGT)

Casandra

Casandra Test Code LC33657Version 1 (DRAFT)

Performing Lab

Lab LabcorpLab Test ID 001958CPT Code 82977

γ-Glutamyl Transferase (GGT)

Also known as: Gamma-Glutamyl Transferase, Glutamyl Transpeptidase

Clinical Use

Order Test

Use

A biliary enzyme that is especially useful in the diagnosis of obstructive jaundice, intrahepatic cholestasis, and pancreatitis.1 GT is more responsive to biliary obstruction than are aspartate aminotransferase (AST) (SGOT) and alanine aminotransferase (ALT) (SGPT).

Special Instructions

Patients should fast for eight hours prior to specimen collection to avoid false elevations, particularly if on phenytoin or phenobarbital therapy. Alternate tests like leucine aminopeptidase (LAP) or 5' nucleotidase are recommended under such circumstances.

Limitations

GGT levels can be artificially altered by external factors like acetaminophen toxicity which causes an in vivo increase. While GGT can signify liver involvement in metastases, its absence does not entirely rule out liver disease. GGT is not consistently elevated in cases with lymphoma without liver involvement. Additionally, GGT may not indicate metastasis uniformly, as seen in some colorectal carcinoma cases where only 81% of progressive diseases showed abnormal GGT levels.

Test Details

Methodology

Automated Analyzer (Clinical Chemistry)

Biomarkers

γ-Glutamyl Transferase

Analyte

γ-Glutamyl Transferase Level • Concentration / Level • Quantitative (Continuous) (e.g., copies/mL, % expression)

LOINC Codes

Order Codes

2324-2

Result Codes

2324-2

Result Turnaround Time

1 day

Specimen

Serum

Volume

1 mL

Minimum Volume

0.7 mL

Container

Red-top tube, gel-barrier tube, or green-top (lithium heparin) tube.

Collection Instructions

Separate serum or plasma from cells within 45 minutes of collection.

Patient Preparation

The patient should fast for eight hours prior to collection of the specimen. Since there are false elevations in patients on phenytoin and phenobarbital, such patients would be better served with orders for one of the alternate tests − leucine aminopeptidase (LAP) or 5′ nucleotidase.