HP and holoprosencephaly: Serological evaluation with anti-HP immunoglobulin G (IgG) antibody testing is an inexpensive and noninvasive method that is used commonly throughout the world for the diagnosis of HP-related conditions.(9) Because HP IgG antibody titers may remain elevated for 6–12 months after HPE, serological testing to establish HPE should be performed at least 6–12 months post-treatment.(10) Serological testing has also been used in ABC risk classification to evaluate GC risk.(11)