Each state in the United States and most developed countries in the world have programs that test newborns for certain hereditary and metabolic diseases. The number of conditions for which infants are tested varies from state to state. Two of the most commonly performed newborn screening tests are for congenital hypothyroidism and PKU, conditions that can result in severe mental retardation if not recognized and treated within the first few weeks of life.

These tests, as well as other tests that may be offered in your state, are performed by taking a small amount of blood from your baby (usually by a heel prick) and sending it to a laboratory for analysis. The blood specimen is usually drawn before your baby leaves the nursery.

Another blood sample may be taken at your child’s first visit to the doctor’s office, depending on various factors. For example, the initial test results may be unreliable for some conditions if your baby is premature or if your infant’s blood was drawn before 24 hours of age. Because the results of newborn screening tests can take several days to come back from the laboratory, make sure that the hospital knows how to contact you and your baby’s doctor after discharge.

A recently developed technique called “tandem mass spectroscopy” has made it possible to screen newborns for a much larger number of metabolic diseases than was previously possible from a small blood sample. At the time of this writing, most states have either begun offering this test or are considering adding it. If the test is not yet available routinely from their state program, some parents are electing to pay for the test themselves. Speak with your child’s doctor about your options regarding this test.