Interpretive performance was excellent for challenges that included specimens with prominent metabolite elevations and poor for challenges containing specimens with complex or subtle findings such as glutaric acidemia type II (2008B, 85.3%) or isobutyryl-CoA dehydrogenase deficiency (2006B, 75.0%). The gene discussed is ACAD8; the disease is hyperinsulinemic hypoglycemia, familial, 4.