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Newborn Screening Tests

About Newborn Screening

Newborn screening is the practice of testing every newborn for certain harmful or potentially fatal disorders that aren't otherwise apparent at birth.

With a simple blood test, doctors often can tell whether newborns have certain conditions that eventually could cause problems. Although these conditions are rare and most babies are given a clean bill of health, early diagnosis and proper treatment sometimes can make the difference between lifelong impairment and healthy development.

Which Tests Are Offered?

Newborn screening varies by state and is subject to change, especially given advancements in technology. However, the disorders listed here are those usually included in newborn screening programs:

  • phenylketonuria (PKU)
  • congenital hypothyroidism
  • galactosemia
  • sickle cell disease
  • biotinidase deficiency
  • congenital adrenal hyperplasia (CAH)
  • maple syrup urine disease (MSUD)
  • tyrosinemia
  • cystic fibrosis (CF)
  • MCAD deficiency
  • severe combined immunodeficiency (SCID)
  • toxoplasmosis

All newborns will also have a hearing screening.

Phenylketonuria (PKU)

Phenylketonuria (PKU) is a metabolic disorder. Metabolism is the process in the body that converts the fuel from food into energy needed to do everything from moving to thinking to growing. A metabolic disorder is any disease caused by an abnormal chemical reaction in the body's cells.

Babies with PKU are missing an enzyme that's needed to process phenylalanine. Phenylalanine is an amino acid necessary for normal growth in kids and for normal protein use. Amino acids are the "building blocks" for the proteins that make up our muscles and other important parts of our bodies. 

If too much phenylalanine builds up, it damages brain tissue and can cause developmental delay.

When PKU is detected early, feeding an infant a special formula low in phenylalanine can prevent intellectual disability. A low-phenylalanine diet is needed throughout childhood and adolescence and sometimes into adult life. This diet cuts out all high-protein foods, so people with PKU often need to take a special artificial formula as a nutritional substitute. 

Congenital Hypothyroidism

The thyroid, a gland at the front of the neck, releases special chemicals called hormones that control metabolism and growth. These hormones control how fast the body uses up energy and are also key factors in helping kids grow.

Babies with congenital hypothryoidism don't have enough thyroid hormone. The condition can cause slow growth and brain development.

If congenital hypothryoidism is detected early, a baby can be treated with oral doses of thyroid hormone.


Babies with galactosemia lack the enzyme that converts galactose (one of two sugars found in lactose) into glucose, the major source of energy for the body's cells.

For a baby with galactosemia, milk (including breast milk) and other dairy products must be removed from the diet. Otherwise, galactose can build up in the body and damage cells and organs, leading to blindness, severe intellectual disability, growth deficiency, and even death.

Many less severe forms of galactosemia may not require any treatment.

Sickle Cell Disease

Sickle cell disease is a blood disorder that's inherited (meaning it's passed down from parents to their children). It affects a protein in red blood cells called hemoglobin that helps carry oxygen throughout the body.

Red blood cells with normal hemoglobin move easily through the bloodstream because of their rounded shape and flexibility. But sickle cell disease makes red blood cells form into a curved, sickle shape. These cells also become sticky, stiff, and more fragile. This makes it hard for them to move through the bloodstream.

Sickle cell disease can cause pain episodes, damage to vital organs like the lungs and kidneys, and even death. Young children with sickle cell disease are especially prone to certain dangerous bacterial infections, like pneumonia (inflammation of the lungs) and meningitis (inflammation of the brain and spinal cord).

Newborn screening for sickle cell disease can alert doctors to begin antibiotic treatment before infections happen. Newborn screening also helps doctors monitor symptoms more closely and can detect other disorders affecting hemoglobin.

Biotinidase Deficiency

Babies with biotinidase deficiency don't have enough biotinidase, an enzyme that recycles biotin (a B vitamin) in the body. Biotinidase deficiency may cause seizures, poor muscle control, problems with the immune system, hearing loss, intellectual disability, coma, and even death.

If biotinidase deficiency is detected quickly, problems can be prevented by giving the baby extra biotin.

Congenital Adrenal Hyperplasia (CAH)

Congenital adrenal hyperplasia (CAH) is a group of disorders involving hormones produced by the adrenal gland. CAH can affect both boys and girls. It causes the adrenal glands to make excess androgens (male steroid hormones) and, in some cases, not enough of the hormones that regulate the body's salt balance.

Congenital adrenal hyperplasia can affect the development of the genitals and may cause death due to loss of salt from the kidneys. Lifelong treatment through supplementation of the missing hormones manages the condition.

Maple Syrup Urine Disease (MSUD)

Babies with maple syrup urine disease (MSUD) are missing an enzyme needed to process three amino acids needed for the body's normal growth. When these amino acids aren't processed correctly, they can build up in the body. If not detected and treated early, MSUD can cause intellectual disability, physical disability, and even death.

MSUD makes urine (pee) smell like maple syrup or sweet, burnt sugar. Babies with MSUD usually have little appetite and are very irritable.

A carefully controlled diet that cuts out certain high-protein foods containing the three amino acids can prevent MSUD. Babies with MSUD are often given a formula that supplies the necessary nutrients.


Babies with tyrosinemia have trouble processing the amino acid tyrosine. If tyrosine builds up in the body, it can cause mild intellectual disability, language skill difficulties, liver problems, and even death from liver failure.

Treatment for tyrosinemia requires a special diet and sometimes a liver transplant. Early diagnosis and treatment can offset long-term problems. 

Cystic Fibrosis (CF)

Cystic fibrosis (CF) is a genetic disorder that mainly affects the lungs and digestive system and makes kids who have it more vulnerable to lung infections. There is no known cure for cystic fibrosis — treatment involves trying to prevent serious lung infections (sometimes with antibiotics) and providing adequate nutrition.

Early detection may help doctors reduce the problems associated with cystic fibrosis, but the real impact of newborn screening has yet to be determined.

MCAD Deficiency

MCAD (medium chain acyl CoA dehydrogenase) is an enzyme needed to break down certain fatty acids in the body. Fatty acids are the building blocks of the fat in our bodies and in the food we eat. During digestion, the body breaks down fats into fatty acids, which can then be absorbed into the blood.

With MCAD deficiency, the body can't process these fatty acids. Kids who have MCAD deficiency can have repeated episodes of low blood sugar (hypoglycemia), which can cause seizures and interfere with normal growth and development.

Treatment for MCAD deficiency involves making sure kids don't fast (skip meals) and that they get extra nutrition (usually by intravenous [IV] nutrients) when they're ill.

Severe Combined Immunodeficiency (SCID)

Severe combined immunodeficiency (SCID) is a serious immune system disorder that happens because of a lack of both B- and T- lymphocytes in the body. Made in the bone marrow and the thymus gland, B- and T- lymphocytes are specialized white blood cells that fight infection. When the immune system doesn't work correctly, it can be difficult or impossible for it to battle viruses, bacteria, and fungi that cause infections.

Early diagnosis of SCID can allow treatment to help the immune system work properly.


Toxoplasmosis is an infection by a tiny parasite (Toxoplasma gondii) that can live inside the cells of humans and animals, especially cats and farm animals.

Toxoplasmosis can cause serious problems in a baby, including seizures and severe eye problems (including blindness) and brain damage or intellectual disability.  

Only a few states in the U.S. screen for toxoplasmosis.

Hearing Screening

Most states require that newborns have their hearing screened before they're discharged from the hospital. If your baby isn't examined then, be sure that your little one gets screened within the first 3 weeks of life.

Kids develop critical speaking and language skills in their first few years. A hearing loss that's caught early can be treated to help prevent problems with that development.

Should I Request Other Tests?

If you answer "yes" to any of these questions, talk to your doctor and perhaps a genetic counselor about additional tests:

  • Do you have a family history of an inherited disorder?
  • Have you previously given birth to a child who's affected by a disorder?
  • Did an infant in your family die because of a suspected metabolic disorder?
  • Do you have another reason to believe that your child may be at risk for a certain condition?

How Screening Is Done

In the first 2 or 3 days of life, your baby's heel will be pricked to get a small blood sample for testing. Most states have a state or regional laboratory do the analyses, although some use a private lab.

It's generally recommended that the blood sample be taken after the first 24 hours of life. However, because mothers and newborns are often discharged within a day, some babies may be tested within the first 24 hours. If this happens, experts recommend that a repeat sample be taken no more than 1 to 2 weeks later. Some states routinely do two tests on all infants.

Getting the Results

Different labs have different procedures for notifying families and doctors of the results. Some may send the results to the hospital where your child was born and not directly to your child's doctor, which may mean a delay in getting the results to you. Ask your doctor how you'll get the results and when you should expect them.

If a test result comes back abnormal, try not to panic. This does not necessarily mean that your child has a disorder. A screening test is not the same as diagnostic test. The initial screening provides only early information that must be followed up with more specific testing.

If testing confirms that your child does have a disorder, your doctor may refer you to a specialist for further evaluation and treatment. Keep in mind that dietary restrictions and supplements, along with proper medical supervision, often can prevent most of the serious physical and mental problems that were associated with metabolic disorders in the past.

You also may wonder whether the disorder can be passed on to any future children. Talk with your doctor and perhaps a genetic counselor. Also, if you have other children who weren't screened for the disorder, consider having testing done. 

Know Your Options

There are no national standards for newborn screening in the United States. Screening requirements vary from state to state and are chosen by each state's public health department. However, almost all states now screen for more than 30 disorders. Many states have mandatory newborn screening programs, but parents can refuse the testing for their infant if they choose.

Learn about what tests are routinely done in your state and in the hospital where you'll deliver (some hospitals go beyond what's required by state law). If your state doesn't offer a particular test, ask your doctor about supplemental screening. Talk to your doctor or contact your state's department of health for more information.

If you're concerned about whether your infant was screened for certain conditions, ask your child's doctor for information about which tests were done and whether further tests are recommended.

Date reviewed: October 2016