Answer

d. INR

Of the above, only the INR is a true liver function test as it examines the capacity of the liver to synthesize clotting factors. AST and ALT are enzymes that are elevated in hepatocellular injury. Alkaline phosphatase is an enzyme that is elevated in cholestatic injury. Bilirubin is a pigment secreted by the liver that is elevated with liver dysfunction but can also be elevated with bile obstruction (even though liver function is normal).