A 64-year-old man complains of abdominal pain, pruritus, 4-lb weight loss, and anorexia. There are multiple scratch marks on the skin of the extremities and flank. The bilirubin is 1.0 mg/dL. To determine if the condition is due to cholestasis, blood should be tested for which of the following?

Pruritus occurs frequently in untreated obstructive jaundice. Bile salt elevation is a possible cause of pruritus. Patients with generalized pruritus should have alkaline phosphatase levels determined; if levels are elevated, the possibility of cholestatic jaundice should be considered. Bilirubin is not always elevated in obstructive jaundice.