Testing for inborn errors of metabolism in the acutely ill newborn.

The differential diagnosis of the acutely ill newborn should include inborn errors of metabolism along with much more common conditions such as sepsis and hypoxemia. Testing recommendations, which can take place simultaneously with other studies, are presented for the evaluation of inborn errors in acutely ill newborns. Initial hospital-based tests include arterial blood gases, glucose, electrolytes, urinalysis, complete blood count, and cultures. The results from these initial tests are used to categorize the clinical presentation into one of several categories, and each category in turn serves to direct further testing in an efficient manner. Definitive diagnosis often requires referral to a pediatric specialist, as well as testing available only through reference and research laboratories. Transfer to a tertiary care facility may be advisable when evidence for an inborn error is found.