A day or two after your baby is born, while still in the hospital, she’ll (briefly) leave your bedside for a blood draw from her heel, known as the heel-stick test.
While the procedure itself is quick, the purpose is important: This first test screens for serious metabolic disorders that can go undetected in newborns but cause serious health problems in the weeks, months or years to come. Here’s what to know about these conditions and how they’re managed.
What are metabolic disorders?
Metabolic disorders are rare conditions that affect the way the body uses food and converts it into energy or fuel. Some can be serious and, when left untreated, have the potential to affect a baby’s health and development.
Under normal circumstances, food (or breast milk or formula) is ingested and broken down, or metabolizes, by enzymes in the digestive tract. This process turns the food into needed sugars and acids that the body can use for energy right away or store for later.
When a baby has a metabolic disorder, the digestive system can’t break down the food correctly. That can result in the body having too much or too little of certain substances, such as amino acids, phenylalanine and blood sugar, which can lead to health problems.
Types of metabolic disorders
There are hundreds of different metabolic disorders, a large number of which are screened for shortly after birth. Some of the metabolic disorders that newborn tests commonly look for include:
- Phenylketonuria (PKU): Babies with this condition can’t metabolize the amino acid phenylalanine, which is found in high-protein foods like breast milk, cow’s milk and meat. Untreated, a buildup of this amino acid in the bloodstream can affect brain development and lead to intellectual and developmental disability. About 1 in 10,000 to 15,000 newborns in the United States is diagnosed with PKU each year.
- Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency: Babies with MCAD deficiency are unable to convert certain fats into energy, which can lead to lethargy and low blood sugar if left untreated. When untreated, MCAD can potentially cause seizures and damage to the liver or brain. About 1 in 17,000 babies in the U.S. is diagnosed with MCAD deficiency each year.
- Galactosemia: Babies with this disorder can’t convert galactose (a milk sugar) into glucose (sugar in the blood). When galactose builds up in a baby’s system it can damage the liver, kidneys, eyes and brain. It’s very rare, affecting just 1 in 30,000 to 60,000 babies in the U.S. each year.
- Citrullinema: This disorder causes ammonia and other toxic substances to build up in the blood stream, eventually leading to lethargy, poor growth and liver problems if left untreated. Around 1 in 57,000 babies worldwide are affected each year.
- Argininosuccinic aciduria: Like citrullinemia, this condition causes ammonia to build up in the blood, which can affect a baby’s nervous system when left untreated. Roughly 1 in 70,000 to 218,000 babies are affected annually.
- Methylmalonic acidemia: This condition occurs when the body is unable to process certain proteins and fats. The effects can range from mild (such as increased lethargy) to severe (like organ damage or failure to gain weight) without treatment. Methylmalonic acidemia occurs in roughly 1 in 50,000 to 100,000 babies each year.
- Tyrosinemia: Tyrosinemia happens when the body is unable to break down the amino acid tyrosine. When left untreated, tyrosine can then build up in the body and contribute to developmental challenges. The condition is rare, occurring in 1 out of 100,000 to 120,000 babies worldwide each year.
- Maple-syrup urine disease (MSUD): Babies with MSUD are missing an enzyme needed to metabolize three essential amino acids needed for growth. Without treatment, this can cause the amino acids to build up in the blood, leading to intellectual disabilities and other health problems. (The disorder gets its name from the fact that it can cause a person’s urine to smell sweet, or like maple syrup.) It’s exceedingly rare, affecting 1 in 185,000 babies each year worldwide.
- Homocystinuria: This is another type of metabolic disorder marked by an inability to break down certain amino acids. The effects can vary, and without screening, some cases can go undetected until later in childhood or adulthood. It occurs in just 1 out of 200,000 to 355,000 people worldwide each year.
What causes metabolic disorders?
Most metabolic disorders occur when a baby is missing a digestive enzyme that’s needed to properly break down food. They’re usually inherited genetic mutations — meaning if a parent has a family history of a metabolic disorder, their baby has a higher chance of having one as well.
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Symptoms of metabolic disorders in babies
Most infants with metabolic disorders appear perfectly healthy when they’re born. Depending on the disorder, they might start to show symptoms days, months or sometimes even years after birth. That’s why screening newborns early — before they start showing signs of possible problems — is so important.
Symptoms vary based on the specific disorder. In many cases, early signs might include lethargy, poor feeding, vomiting, poor weight gain and even seizures.
What happens during a newborn metabolic screening?
Metabolic screenings are performed when babies are 1 or 2 days old, before they leave the hospital. Conducting these tests early can help doctors and families catch and treat metabolic disorders as soon as possible, often before a baby even shows symptoms. If you delivered at a birthing center or at home, it's important to have a pediatrician perform this test within the first few days of your baby's life.
Though newborn metabolic screenings look for a wide range of disorders, the process itself is simple. Within a day or two of being born, a newborn’s heel is pricked in order to draw blood that’s sent to a lab for analysis. If the screening reveals any abnormalities, you’ll be notified within five to seven days and sent for follow-up testing. (If the screening comes back normal, you probably won’t hear anything.)
The U.S. Department of Health and Human Services (HHS) recommends 35 core disorder and 26 secondary disorder screenings, for a total of up to 60 newborn tests. Not every state requires all of these screenings, but all U.S. babies are required by laws mandated by the state where they’re born to receive a blood draw for metabolic, genetic, hormonal and functional disorders — typically primarily those on the recommended HHS list, but some states test further for other possible, additional disorders.
You can find out which conditions are screened for in your state at Baby’s First Test and Baby’s First Test en Español.
Treatment for metabolic disorders
Many metabolic disorders are treatable, and starting treatment sooner rather than later can help prevent serious health risks.
In many cases, children with metabolic disorders can stay healthy by avoiding certain foods. For instance, babies with PKU can avoid complications if they eat a phenylalanine-free formula and a diet low in high-protein foods. Babies with galactosemia can avoid complications by eliminating dairy products (which contain lactose) and drinking soy-based formula instead. Babies with MCAD deficiency can stay healthy by consuming a special formula and eating frequently, just as babies with MSUD (who can’t metabolize certain amino acids) must eat a special diet.
Some children might also need to take supplements or medications.
That said, different metabolic disorders are treated differently, so the care a child receives will depend on her diagnosis as well as the severity of her disorder. Working with your child’s pediatrician as well as specialists can help your little one get the care that she needs.
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