When a child is born with a serious health condition, families want answers fast. With congenital adrenal hyperplasia (CAH), getting the right diagnosis early can be lifesaving. Most babies with the classic form are identified through newborn screening tests done in the first days of life. In families with a history of CAH, doctors can also test during pregnancy.

However, not all types of CAH show up right away. Some milder forms, like nonclassic CAH, may not cause symptoms until later in childhood, adolescence, or early adulthood.

Testing is also used after diagnosis to monitor hormone levels and check treatment effectiveness. Knowing what tests doctors use and what the results mean can help you feel prepared during every step along the way.

When Do Doctors Test for CAH?

The two main types of CAH are classic and nonclassic. Classic CAH is more serious and is typically found through newborn screening. Nonclassic CAH tends to be milder and shows up later in life.

Classic CAH is divided into two subtypes: salt-wasting and simple-virilizing. The salt-wasting form can cause life-threatening adrenal crises due to the body’s inability to retain salt and water, leading to dehydration, low blood pressure, and shock. The simple-virilizing form does not involve salt-wasting.

If you or your child wasn’t diagnosed at birth, a doctor might want to run tests for CAH for several reasons. Some people have high levels of certain sex hormones (androgens), along with other CAH symptoms. Other people might have a child or another family member who was recently diagnosed with CAH. Doctors or genetic counselors can offer testing to see if you’re at risk of passing this condition to your children.

CAH affects the adrenal glands — tiny organs that play a major part in controlling the body’s hormone balance. The adrenal glands sit on top of the kidneys and produce aldosterone, cortisol, and androgens. People with CAH don’t make enough of an enzyme called 21-hydroxylase, a specialized protein that’s needed to make the adrenal hormones.

If you or your child is experiencing CAH symptoms, your doctor can perform several tests to make a diagnosis. To avoid health complications, it’s important to stick with your treatment plan after you’re diagnosed.

Types of Testing for CAH

Some tests identify genetic mutations (changes), whereas others check hormone levels or bone development. Each test provides doctors with vital information about your condition, whether you’re getting an initial diagnosis or monitoring your treatment and health over time.

1. Genetic Testing

Genetic testing takes a close look at DNA to find genetic mutations in cells. Most people with CAH have changes in the CYP21A2 gene, which provides instructions for making 21-hydroxylase. A healthcare provider takes a small blood sample to perform genetic testing. The sample is sent to a lab and checked for specific CYP21A2 changes.

Different changes in the CYP21A2 gene help explain why some people develop classic CAH and others get the nonclassic form. In classic CAH, the mutations are more severe and almost completely block the production of the 21-hydroxylase enzyme. In nonclassic CAH, the mutations only partly reduce enzyme activity.

You may undergo genetic testing if you have symptoms of CAH and problems with infertility. Your doctor can also recommend testing if you have unusually high androgen levels. People who have family members with CAH can also get tested to find out if they carry a mutated CYP21A2 gene that could affect their children.

2. Prenatal Testing for CAH

CAH is a genetic condition passed down from parents to their children. Everyone inherits two sets of chromosomes: one from their mother and the other from their father. To develop CAH, you need to inherit two nonworking copies of the CYP21A2 gene. This is called an autosomal recessive pattern of inheritance.

Doctors or genetic counselors may recommend prenatal testing if:

• You already have one child who has CAH.
• You or your partner is a known carrier of CYP21A2 (has one mutated copy of the gene).
• You or your partner has CAH (two mutated copies).

If any of these statements apply to you, you’re more likely to pass CAH to your child. Doctors can do prenatal testing to check if the fetus has CAH. The two options for these tests are chorionic villus sampling and amniocentesis.

For chorionic villus sampling, a doctor inserts a needle into the womb through the cervix or abdomen and then guides the needle to the chorionic villi — projections of tissue that eventually become the placenta that supports the growing fetus. A small piece of tissue is removed and tested for gene changes. This test must be performed in the 10th to 12th week of pregnancy.

During amniocentesis, a needle is inserted into the abdomen to take a sample of amniotic fluid surrounding the fetus. The fluid is sent to a lab for genetic testing. Doctors typically perform this test in the first 15 to 20 weeks of pregnancy. Both types of prenatal genetic testing carry a small risk of miscarriage at about 0.5 percent.

3. Newborn Screening Test

In the United States, newborn testing includes screening for CAH. A healthcare professional takes a small blood sample from the baby’s heel. The sample is sent to a lab to measure levels of 17-hydroxyprogesterone (17-OHP).

Your baby’s 17-OHP levels may be high if they’re not making enough of the hormone cortisol. People with CAH have more 17-OHP in their blood because they’re missing the enzyme 21-hydroxylase.

If the results show high 17-OHP levels, your baby will need more testing to confirm CAH and rule out other conditions. Many factors, such as stress, low birth weight, prematurity, or illness, can also raise 17-OHP, so a positive result doesn’t always mean CAH. Doctors often repeat the test or order additional blood tests, urine tests, or genetic testing to confirm the diagnosis.

Newborn screening tests identify only classic CAH. Infants with nonclassic CAH are typically diagnosed as children or adults. The sections below discuss these tests.

4. Physical Exam

For people whose potential CAH symptoms develop later, doctors may use physical exams to check for signs. CAH causes elevated androgen levels, and people with the condition tend to have specific sets of symptoms that point to a diagnosis. Symptoms depend on the type of CAH.

According to Cleveland Clinic, female infants with classic CAH may have internal organs like ovaries but atypical external genitalia. The clitoris may be larger than normal, and the labia may be fused partially or fully together. A male infant with CAH may have an enlarged penis.

Children and teenagers with classic CAH will also have specific symptoms. Many experience early puberty, with facial, armpit, and pubic hair appearing sooner than usual. Females may develop certain characteristics, such as a deep voice or larger muscles.

Nonclassic CAH is milder than classic CAH, and the symptoms may look different in a physical exam. Nonclassic CAH tends to cause:

• Early signs of puberty
• Acne
• Hair loss on the scalp
• Increased facial and body hair
• Small testicles and an enlarged penis

5. Urine Test

The hormone aldosterone is key to maintaining the body’s fluid and electrolyte balance. Some people with classic CAH get rid of too much sodium and not enough potassium. This is why you may hear some types of classic CAH referred to as “salt-wasting.” Your doctor can run a quick urine test to measure how much sodium and potassium your kidneys are getting rid of.

6. X-Rays for Bone Age

Children’s bodies are constantly growing. During puberty, growth plates at the ends of long bones in the arms and legs turn into solid bone tissue. When growth plates close, a person stops growing.

Children with CAH grow much faster than those who don’t have the condition. Your child’s doctor may take X-rays of the pelvis, wrists, and hands to check whether their growth plates have closed early. These bone age studies also help track your child’s growth and show how well their CAH treatment is working over time.

7. Adrenocorticotropic Hormone Stimulation Test

The adrenocorticotropic hormone (ACTH) stimulation test may be used to check how the adrenal glands are working. ACTH tells the adrenal glands to release cortisol. Your doctor may recommend an ACTH stimulation test if:

• You have low cortisol levels.
• You may have CAH.
• You’ve been taking glucocorticoid medicines for a long time.

A healthcare provider will take a blood sample to measure your baseline hormone levels, and then you’ll receive an injection of ACTH to stimulate your adrenal glands. After an hour, the provider will take another blood sample to see if the injected ACTH led to changes in your androgen and 17-OHP levels.

During ACTH stimulation, people with classic CAH have very high levels of 17-OHP and androgens. Levels for people with nonclassic CAH will also be elevated, but not as much.

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