This patient requires no further tests for his scleral icterus. He has an indirect hyperbilirubinemia with normal liver enzyme levels, reticulocyte count, and blood smear. These findings are consistent with Gilbert syndrome, and no further tests are necessary. Gilbert syndrome is a benign condition characterized by mild unconjugated hyperbilirubinemia, which is caused by a congenital decrease in hepatic uridine diphosphate glucuronyl transferase. Patients with Gilbert syndrome have a defect in the ability to conjugate bilirubin, resulting in unconjugated hyperbilirubinemia. The bilirubin level tends to be highest when the patient is fasting or ill but is usually less than 3 mg/dL (51.3 µmol/L).

Patients with warm autoimmune hemolytic anemia (WAIHA) may present with rapid or more insidious symptoms of anemia or jaundice; mild splenomegaly is often present. Spherocytes are seen on the peripheral blood smear. The direct antiglobulin (Coombs) test is used to diagnose WAIHA and is typically positive for IgG and negative or only weakly positive for complement (C3). Hemolytic anemia is associated with a low hemoglobin level, a high reticulocyte count, and an abnormal blood smear. Because these features are not present in this patient, there is no need for further hematologic evaluation with a direct antiglobulin (Coombs) test.

Hepatitis is associated with hepatocyte inflammation and injury typically manifested as elevations of serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT). This patient's laboratory abnormality is limited to unconjugated hyperbilirubinemia, which is not consistent with either hepatitis B or C; serologic screening for these conditions is unnecessary.

Primary sclerosing cholangitis (PSC) is a chronic inflammatory disorder that affects the intra- and extrahepatic bile ducts. Serum alkaline phosphatase values are 3 to 10 times the upper limit of normal, and serum ALT and AST levels are two to three times the upper limit of normal. The diagnosis is made by cholangiography. This patient's solitary finding of unconjugated hyperbilirubinemia is not compatible with the diagnosis of PSC.