GGT — Normal Range & Interpretation

Clinical Context

Gamma-glutamyl transferase (GGT) is an enzyme concentrated in the liver, biliary tract, pancreas, and kidneys. It catalyzes the transfer of glutamyl groups and serves as a sensitive marker of hepatobiliary dysfunction, particularly cholestasis. Clinicians pair GGT with alkaline phosphatase (ALP) to confirm that an elevated ALP originates from the liver rather than bone, making it a key clarifying test on the hepatic panel.

Elevations occur with chronic alcohol use, biliary obstruction, cholangitis, cholestatic liver disease, nonalcoholic fatty liver disease, and hepatotoxic medications such as phenytoin, carbamazepine, and statins. GGT also rises with pancreatic disease and heart failure causing hepatic congestion. Low or normal GGT with an elevated ALP points toward a bone source. GGT lacks a clinically significant low value.

What the AANP exam actually tests on GGT: its role as a discriminator — when ALP is elevated, a concurrently elevated GGT confirms hepatobiliary origin, while a normal GGT redirects the workup toward bone pathology such as Paget disease or metastases. Expect questions linking isolated GGT elevation to chronic alcohol use, since GGT is the most sensitive marker for heavy drinking. Candidates should also recognize GGT elevation alongside AST and ALT in suspected medication-induced liver injury and cholestatic patterns.

Related Labs

• AST (SGOT) — U/L
• ALT (SGPT) — U/L
• ALP — U/L
• Total Bilirubin — mg/dL
• Direct Bilirubin — mg/dL

Sources

• MedlinePlus
• ARUP Consult