Newborn screening is a public health service done in each U.S. state. Every newborn is tested for a group of health disorders that aren’t otherwise found at birth. With a simple blood test, doctors can check for rare genetic, hormone-related, and metabolic conditions that can cause serious health problems. Newborn screening lets doctors diagnose babies quickly and start treatment as soon as possible. Most states also screen for hearing loss and critical congenital heart disease, which are not done by testing the blood.