Gilbert's Syndrome: A benign condition characterized by a mild increase in unconjugated bilirubin due to reduced activity of the enzyme uridine diphosphate glucuronyltransferase. It's often asymptomatic and discovered incidentally, which aligns with the normal CT scan findings.

Hemolytic Anemia: Conditions such as autoimmune hemolytic anemia, hereditary spherocytosis, or glucose-6-phosphate dehydrogenase (G6PD) deficiency can lead to elevated bilirubin levels due to increased red blood cell breakdown. A normal CT scan doesn't rule out these conditions, as they primarily affect the blood and bone marrow.
Viral Hepatitis: Acute viral hepatitis (e.g., hepatitis A, B, or C) can cause elevated bilirubin levels. Early in the disease or in mild cases, the liver may appear normal on CT scan.
Alcoholic Liver Disease: Early stages of alcoholic liver disease, such as alcoholic hepatitis, can present with elevated bilirubin without significant abnormalities on CT scan.

Hepatic Artery Thrombosis or Embolism: Although less common, these conditions can lead to liver dysfunction and elevated bilirubin. A normal CT scan might not capture the thrombosis or embolism, especially if it's early or in a small branch of the hepatic artery. Missing this diagnosis could lead to severe liver damage or death.
Budd-Chiari Syndrome: This condition, characterized by thrombosis of the hepatic veins, can cause elevated bilirubin and liver dysfunction. It might not be evident on a CT scan, especially if the thrombosis is not extensive. It's a critical diagnosis to consider due to its potential for severe complications.

Dubin-Johnson Syndrome: A rare genetic disorder causing chronic jaundice due to an inability to secrete conjugated bilirubin into the bile. It's characterized by a distinctive black liver due to the accumulation of epinephrine metabolites, which might not be visible on a standard CT scan.
Crigler-Najjar Syndrome: A rare congenital disorder affecting the enzyme responsible for bilirubin conjugation, leading to very high levels of unconjugated bilirubin. It's usually diagnosed in infancy but could be considered in rare cases of unexplained jaundice in adults.
Zellweger Spectrum Disorders: A group of rare, genetic disorders affecting the breakdown of fatty acids and amino acids, which can lead to elevated bilirubin among other symptoms. These disorders are typically diagnosed in infancy or early childhood but could be considered in cases of unexplained liver dysfunction.