What is the most appropriate next step for a 6-week-old infant with symptoms including jaundice and an enlarged abdomen?

In the case of a 6-week-old infant presenting with jaundice and an enlarged abdomen, the immediate concern often revolves around identifying any underlying conditions that could be causing these symptoms. Jaundice in infants can be indicative of several issues, including liver dysfunction, hemolytic disease, or metabolic disorders. An enlarged abdomen can suggest hepatomegaly or other visceral enlargement related to these conditions.

Performing thyroid function studies is particularly relevant in this scenario because congenital hypothyroidism can cause jaundice and abdominal distension due to an accumulation of toxic metabolites, which can result from insufficient thyroid hormone levels. This condition is one of the newborn screenings that are critical to evaluate if unexplained jaundice and abdominal issues present. Thyroid function studies would help in determining whether the jaundice is secondary to thyroid dysfunction, thus guiding further management.

Other options may not address the immediate need to rule out serious underlying conditions. For example, administering nutritional supplements or providing symptomatic relief could be useful in managing symptoms but may not be sufficient if a significant underlying disease is present. Confirming previous vaccinations does not directly relate to the immediate symptoms of jaundice and abdominal enlargement, as vaccination history will not alter the acute management of these clinical signs.