What is the most likely diagnosis for a patient with 2.5 mg/dL bilirubin and normal liver enzyme levels?

The most likely diagnosis for a patient presenting with a bilirubin level of 2.5 mg/dL and normal liver enzyme levels is Gilbert's syndrome. This condition is characterized by an isolated increase in unconjugated (indirect) bilirubin due to a genetic deficiency in the enzyme responsible for bilirubin conjugation in the liver.

In Gilbert's syndrome, the bilirubin level can fluctuate, and patients often present with mild jaundice but typically have normal liver function tests, as indicated by the normal liver enzyme levels. The diagnosis of Gilbert's syndrome is confirmed when these findings are consistent and there is no other underlying liver disease. The relatively low level of bilirubin, alongside normal liver enzymes, aligns well with typical presentations of this benign condition, making it the most plausible diagnosis in this scenario.

In contrast, conditions such as hemochromatosis, cholecystitis, or hepatitis would generally manifest with abnormal liver function tests or additional clinical symptoms. Thus, the presentation you provided is most compatible with Gilbert's syndrome, confirming it as the most likely diagnosis.