Which pattern on liver function tests indicates a cholestatic injury?

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Cholestatic injury shows a distinctive pattern on liver tests: the alkaline phosphatase (ALP) rises markedly, often with a concurrent rise in gamma-glutamyl transferase (GGT), while the aminotransferases (ALT and AST) are only modestly elevated. ALP comes from bile duct epithelium, so when bile flow is impaired or there’s biliary injury, these cells produce more ALP. GGT is elevated in liver/biliary disease and helps confirm a hepatic source of the ALP rise, since ALP from bone wouldn’t usually elevate GGT. In contrast, a hepatocellular pattern features much higher ALT/AST relative to ALP, reflecting direct injury to hepatocytes rather than the biliary tree. So the combination of high ALP and GGT with only modest transaminase elevations is the hallmark of cholestasis.