While newborn screening tests are likely to find newborns with the diseases, like all tests, they are not perfect. Sometimes they incorrectly report a disease a child does not actually have. Therefore, all children who test positively for a disease should be tested again. Rarely, the tests do not identify children that actually do have the disease. Hypothyroidism and phenylketonuria can cause mental retardation if they are not treated.
Most states also test for disorders of hemoglobin, including sickle cell disease.
If these rare diseases are diagnosed and treated early, they can be improved or possibly cured. The tests are run on small amounts of blood obtained by making a tiny cut in the baby's heel. Well infants are usually tested just before they go home from the hospital, but not later than 72 hours after birth. If a test does suggest your child has a disease, the health department will contact you and your baby's doctor. If the tests do not show any diseases, you will generally not be contacted.