What happens if a newborn screening test comes back positive?

Within 2 to 3 weeks after newborn screening tests are performed, results are sent to the baby's doctor’s office or clinic. A positive result means that at least one of the tests came back outside the normal range. Other words for a positive result are "failing," "out-of-range," or "abnormal."
The healthcare provider will notify parents of a positive test result. A positive result does not mean that a baby definitely has a disease, but it indicates that further testing (called diagnostic testing on page 187, because it is used to diagnose a disease) should be performed as soon as possible. If the baby does have the disease, quick follow-up testing can allow treatment or management , such as a special diet, to begin very soon after birth.
Often when there is a positive screening test result, follow-up diagnostic testing shows that the baby does not have the disease. In these cases, the results of the newborn screening test are described as "false positive," meaning that the test suggested an increased risk of the disease when the baby does not actually have the disease. False positive test results occur because screening tests are designed to identify as many babies affected with treatable diseases as possible.
Because it is critical not to miss affected babies, some babies who are unaffected also have a positive screening result. Occasionally, the results of a newborn screening test are reported as "borderline." These results are not quite normal, but they are not clearly abnormal, either. In these cases, the baby’s healthcare provider may repeat the
test.