In a patient with cholestatic jaundice, which enzyme ratio would most reliably distinguish intra-hepatic cholestasis from extrahepatic biliary obstruction when imaging is equivocal?

• A ALT/AST ratio >2
• B ALP isoenzyme fractionation showing hepatic vs. bone isoform ✓
• C GGT/ALP ratio elevated with isolated GGT rise
• D LDH/AST ratio

Explanation

ALP exists as liver, bone, intestinal and placental isoforms. Heat-stable ALP (56°C for 15 minutes retains activity) is liver-derived, while heat-labile ALP is bone-derived. ALP isoenzyme fractionation by electrophoresis or differential heat inactivation specifically identifies hepatic ALP. GGT elevation confirms hepatic origin of ALP but does not differentiate intra- from extrahepatic cholestasis. ALT/AST >2 favours alcoholic liver disease, not cholestasis. LDH/AST ratio is not clinically validated for this distinction.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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