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What is being tested?

17-OHP is steroid hormone produced by the adrenal gland as part of the process of making the important hormone cortisol. Several enzymes are required for this process. If a person is born with either not enough of one of these enzymes or an abnormal form of an enzyme, their adrenal gland cannot produce cortisol efficiently. Depending on which enzyme is abnormal, another important hormone, aldosterone may also be affected. In such cases, 17-OHP builds up. Some of the excess 17-OHP is used up by making male hormones (androgens). Excess androgens can cause virilisation, the development of male sexual characteristics, in both females and young males.

These inherited enzyme deficiencies and the resulting excess androgens occur in a group of disorders called congenital adrenal hyperplasia (CAH). Most cases of CAH are caused by a lack of the enzyme 21-hydroxylase. About 90% of CAH cases are caused by a mutation in the 21-hydroxylase gene ( also called CYP-21 or P450c1 or CYP21A2) and may be detected due to the accumulation of 17-OHP in the blood. The disease is caused when both genes,, one from each parent, have mutations that decrease or stop the activity of the enzyme for which the gene codes. Parents may be carriers, and carriers may not have any signs of the disease. 


In more severe forms of CAH, the condition becomes evident in infancy or childhood, while milder forms, known as late-onset or non-classical CAH, may not become evident until later in life, including adulthood. In the more serious form of CAH, excess androgens can cause female babies to be born with ambiguous genitalia, meaning it can be difficult to tell at birth if they are male or female. In less severe forms in females the first sign of the condition may be hirsutism, irregular menstruation or infertility. Males with this condition may start to develop sexual characteristics prematurely in early childhood (precocious puberty) or experience infertility as adults.

In many people with CAH the adrenal gland cannot produce enough of another hormone, aldosterone. Aldosterone prevents the body from losing too much sodium salt and water in the urine. Babies with CAH who have aldosterone deficiency can suffer from life-threatening "salt-wasting" crises and may have low blood sodium levels (hyponatraemia) and high blood potassium levels (hyperkalaemia).

How is it used?

The 17-OHP is the best screening test in children with ambiguous genitalia to detect congenital adrenal hyperplasia (CAH). It may used to aid in the diagnosis of CAH in older children and adults who may have a milder, "late-onset" form.
CAH will also produce less aldosterone, a hormone that regulates the retention of salt. The loss of too much fluid and salt in the urine can lead to a life-threatening adrenal crisis also called "salt-wasting" crises.

Positive 17-OHP screening tests may be repeated, or other tests performed, such as androstenedione and testosterone. If a 17-OHP test is abnormal, then an ACTH stimulation test may be also be ordered as a follow-up test. In CAH, ACTH stimulation will markedly increase 17-OHP levels. Genetic testing may be performed to detect CYP21A2 gene mutations that can cause the condition. A karyotype test may be ordered as a follow-up test to detect chromosome disorders and to help determine a baby's sex. Electrolytes may be ordered to measure the person's sodium and potassium levels.

If someone is diagnosed with CAH, hormonal treatment may be required, such as cortisol treatment, and a 17-OHP test may be used periodically to monitor the effectiveness of this treatment.

A 17-OHP test may also sometimes be used, along with other hormone tests, to help rule out CAH in women with symptoms of androgen excess, such as hirsutism, irregular periods. This includes women with suspected polycystic ovarian syndrome (PCOS) and infertility, and rarely those suspected of having an adrenal or ovarian tumour.

When is it requested?

A 17-OHP test may be ordered whenever an infant has signs of virilisation, experiences a salt-wasting crisis or has other signs of abnormal functioning of the adrenal gland (adrenal insufficiency). Some signs and symptoms may include:

  • Listlessness, lack of energy (lethargy)
  • Not eating well
  • Dehydration
  • Low blood pressure
  • Sex organs that are not clearly male or female (ambiguous genitalia)

This test may sometimes be ordered in older children or in adults when the milder form of CAH (late-onset) is suspected. The 17-OHP test may also be conducted when a girl or woman is experiencing symptoms such as:

  • Hirsutism
  • Lack of or irregular periods (menses)
  • Virilisation
  • Infertility

In women, the symptoms are very similar to those of polycystic ovarian syndrome (PCOS).

Boys or men may experience:

  • Early (precocious) puberty
  • Infertility

When a person has been diagnosed with 21-hydroxylase deficiency, then a 17-OHP test may be ordered periodically to monitor the effectiveness of treatment.

What does the result mean?

If a newborn or infant has significantly elevated concentrations of 17-OHP, then it is likely that he or she has CAH. If a person has moderately increased levels, then they may have a less severe case of CAH or an 11-beta-hydroxylase deficiency ( another enzyme defect that is associated with CAH) or may have a false positive test.

Normal 17-OHP results mean that it is likely that the person does not have CAH due to a 21-hydroxylase deficiency. In a person being treated for CAH, a low or decreasing level of 17-OHP indicates the treatment is working while a high or increasing level may indicate that changes in treatment are required.

Is there anything else I should know?

Premature infants often have elevated levels of 17-OHP. The test may need to be repeated at a later time.

Rarely, prenatal 17-OHP testing may be performed on amniotic fluid to detect and treat CAH in the fetus during pregnancy.

Common questions

  • Can I have CAH if no CYP21A2 gene mutations were detected during genetic testing?

Yes. Testing detects the most common mutations but will not detect those that are rare. If a specific mutation has been identified in your family line, then you should be tested for that mutation. Also, this test only detects CAH due to 21-hydroxylase deficiency. Other less common types of CAH will not have mutations in the CYP21A gene.

  • Can I have CAH with no symptoms of virilisation?

Yes. You may have a very mild deficiency or you may have CAH that is due to a different enzyme defect.

  • If I have CAH, or my child does, should my family members be tested?

You should talk to your healthcare practitioner or a genetic counsellor about this. Since CAH is caused by an autosomal recessive genetic mutation, both parents must have an altered gene in order for a child to have the condition. If both parents are carriers then each child has a 25% chance of having the condition.

  • Is 21-hydroxylase deficiency CAH curable?

No, but it is treatable. Those with the condition will need to take glucocorticoids, and mineralocorticoids if their aldosterone is also low, throughout their life. In times of stress or illness, they may need extra medication to meet the needs of their body.

Last Updated: Thursday, 1st June 2023

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