Why Do They Prick Your Newborn Baby’s Heel?

PKU or blood spot test finds hidden conditions early when treatment can be initiated

When your baby is born, there are many firsts: a first breath outside the womb, a first touch. If your baby is born in a hospital, they will also receive their first series of health screenings.

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Every state in the United States requires newborns to have certain health tests. A hearing test is required by law in certain states, for example, and a pulse oximetry test determines the level of oxygen in an infant’s blood. An abnormal oxygen level can indicate a critical heart malformation.

About 24 hours after your baby is born before you’re discharged from the hospital, a nurse will administer a “heel prick” test to look for indications in the blood of rare medical conditions such as phenylketonuria or PKU. We asked pediatrician Thomas Phelps, MD, what else parents need to know about the newborn screening panel.

Why does your newborn need a blood test?

Newborn screening got its start in the 1960s when scientists developed a blood test for PKU, an amino acid disorder. “Babies with PKU appear perfectly healthy at first,” says Dr. Phelps. “But if their condition isn’t treated soon after birth by changing their milk supply, they will eventually experience a host of serious health issues including the possibility for developmental delays, brain damage and even death,” he says.

Over time, states added tests (Ohio has 38 conditions tested) for other conditions besides PKU to this heel prick test. In particular, they test for conditions that aren’t obvious at birth and are treatable before it is too late and symptoms appear.

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“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, which can sometimes involve something as simple as a change in diet, can prevent how the disease affects your child as an infant and throughout their whole life,” he says.

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 a hospital, the staff will test your baby before you’re released to go home. If you give birth at home, a midwife should do the test at home 24 hours from birth. “If you have a home birth, you can also take your newborn to a local hospital for the screening 24 hours after they’re born and within 2-3 days,” says Dr. Phelps.

A nurse or medical technician will draw blood from your baby’s heel and send it off to a state lab for testing. “Ideally your infant should have fed prior to the test,” says Dr. Phelps. Your pediatrician will let you know if the screening results show any issues, usually within a week.

But the screening is not a diagnostic tool, Dr. Phelps says. “If anything shows up as abnormal, the test will be repeated to confirm,” says Dr. Phelps. He clarifies: “Some tests will be normal on repeat testing. After the child’s physician or specialist verifies the test results, the specialist will set up a care plan for treatment and close follow up.”

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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 based on population genetics. Most states test for PKU (present in 1 in 10,000-15,000 births), 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 within four weeks of age, 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. As the name suggests, babies with MSUD have a distinctive, sweet-smelling odor to their urine. With this condition, the body is unable to break down certain proteins. Babies with this condition may seem listless or lethargic, exhibit vomiting or poor feeding habits due to nausea and if left untreated, can develop seizures. This condition can eventually be fatal if left untreated. It is so named because the urine of those with MSUD smells like maple syrup.
  • Cystic fibrosis (CF). 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. This condition also hinders a baby’s ability to retain nutrients and grow normally. There is no cure, but early awareness and treatment can help you manage the condition, so your child can live a longer, healthier life.
  • Sickle Cell Anemia. This condition affects people of African descent as well as families from South or Central America, the Caribbean Islands, Mediterranean countries, India and Saudi Arabia. This condition can cause anemia (low red blood cells), fatigue, pain, organ damage and death. Your child’s doctor will also test for other possible problems with their hemoglobin (a protein in your red blood cells). This may include thalassemia (either alpha or beta types), which is genetically passed down to children as sickle cell.

That tiny heel prick can reveal so many illnesses that can potentially be life-threatening or can potentially be physically and intellectually damaging. 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 screenings look for are rare, but sometimes serious,” says Dr. Phelps. “Finding them early offers the best chance for your baby to grow and thrive.”

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