In acute viral hepatitis, bilirubin rises and alkaline phosphatase may be modestly elevated if cholestasis is present.

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In acute viral hepatitis the injury is mainly hepatocellular, so bilirubin rises because the damaged liver cells cannot take up, conjugate, or excrete bilirubin efficiently. Alkaline phosphatase comes from the bile ducts and increases when there is cholestasis, or impaired bile flow. If cholestasis is present in this setting, the ALP level can become quite high because bile obstruction or ductal injury stimulates more ALP release and production. Therefore, seeing bilirubin elevated together with a markedly elevated ALP best reflects hepatocellular injury with concurrent cholestasis.