Why Do They Prick Your Newborn Baby’s Heel?

PKU or blood spot test finds hidden conditions early

When a baby is born, there are many firsts: a first breath outside the womb, a first touch. If your child is born in a hospital, she will get another first — a first bandage. A nurse will whisk her away for a “heel prick” blood test.

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We asked pediatrician Thomas Phelps, MD, what they’re testing for, and what else parents need to know about the newborn screening panel.

Every state in the United States requires newborns to have certain tests shortly after birth. A hearing test is common. And a pulse oximetry test determines the level of oxygen in an infant’s blood. (Low oxygen levels may indicate a serious heart defect.)

The test that can be called the “heel prick,” PKU, or newborn blood spot test provides blood for a screening panel that looks for signs of rare conditions that can affect your baby’s health.

Why does your newborn need a blood test?

Newborn screening got its start in the 1960s when scientists developed a blood test for phenylketonuria (PKU), an amino acid disorder. Babies with PKU appear perfectly healthy at first, but if their condition isn’t treated, they will eventually experience developmental delays.

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Over time, states added tests for other conditions besides PKU. In particular, they test for conditions that:

  • Cause no obvious signs when your baby is born
  • Are treatable

Knowing whether your baby has one of these conditions before symptoms appear can make a huge difference in your baby’s health, Dr. Phelps says. In fact, early treatment — sometimes something as simple as a change in diet — can sometimes prevent the effects of the disease. 

How does the screening work?

In general, doctors arrange for testing when a newborn is between 24 and 48 hours old. If your baby is born in the hospital, the staff will do the testing before you and your baby go home. If you give birth at home, a midwife can do the test at home or you can take your newborn to a local hospital for the screening soon after he or she is born.

A nurse or technician will draw blood from your baby’s heel and use the blood drops for the screening. The blood goes to a lab for testing.

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Your doctor will let you know if the screening results show any issues. But the screening is not a diagnostic tool, Dr. Phelps says. If anything shows up, a specialist will need to verify test results to confirm whether your baby needs further testing or treatment.

What conditions are they looking for?

Each state determines which conditions the newborn screenings will test for, Dr. Phelps says. Health officials typically take into account both national health recommendations and what conditions are most common in each region.

Most states test for PKU, but many also test for:

  • Primary congenital hypothyroidism (CH). This is an endocrine disorder in which your baby’s body doesn’t produce enough of the thyroid hormone. Without treatment, CH can lead to developmental delays and slow growth.
  • Maple syrup urine disease (MSUD). Like PKU, MSUD is an amino acid disorder that can lead to developmental delays. With this condition, the body is unable to break down certain proteins. It is so named because the urine of those with MSUD smells like maple syrup.
  • Cystic fibrosis. This condition affects the mucus glands and causes mucus to be thick and sticky. The mucus prevents certain organs from working properly, including the lungs, liver and intestines. There is no cure, but doctors can help you manage the condition, helping your child lead a longer, healthier life.

Regardless of what conditions your state screens for, hospitals offer the newborn screening panel to help all babies get the best start possible. The conditions it looks for are rare, but sometimes serious. Finding them early offers the best chance for treatment.

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