Substitution of the current indices (C16 + C18:1)/C2 and C14/C3 with C12/C0 is expected to reduce the number of NBS results that are falsely positive for CPT II deficiency in Japan, while adequate sensitivity for the hypoglycemic form will be retained. The gene discussed is CPT2; the disease is hyperinsulinemic hypoglycemia, familial, 4.