The Test Sample
What is being tested?
Pregnenolone is a chemical substance that is a precursor to all steroid hormones. This test measures the amount of pregnenolone in the blood in order to help detect rare forms of congenital adrenal hyperplasia (CAH).
CAH is a group of inherited disorders associated with deficiencies in the enzymes required for the production of the steroid hormones. CAH may be due to:
- 21-hydroxylase deficiency, the most common cause of CAH (about 90% of cases)
- 11-beta-hydroxylase deficiency (about 5-8% of cases)
- 3-beta-hydroxysteroid dehydrogenase and 17-alpha-hydroxylase deficiencies, two rare forms of the disease
- Cortisol, which helps metabolize proteins, lipids, and carbohydrates, maintain blood pressure, and regulate the immune system
- Aldosterone, which maintains normal sodium and potassium levels in the blood and helps control blood volume and pressure
- Sex steroid hormones – including androgens, the "male hormones" such as testosterone, and "female" hormones including estrogen and progesterone, which are responsible for the development and maintenance of male and female secondary sexual characteristics
In congenital adrenal hyperplasia, one or more of the enzymes is deficient or dysfunctional and inadequate amounts of one or more final products are produced. Because a low level of cortisol causes the level of a pituitary hormone that stimulates adrenal growth and hormone production (adrenocorticotropic hormone, or ACTH) to become elevated, the adrenal gland increases in size. However, the increased size and activity cannot overcome the block in cortisol production. Other substances (such as pregnenolone) that do not need the defective enzyme will be produced in excess.
With CAH, the enzyme deficiency can cause a decrease in cortisol and/or aldosterone and, in some cases, an increase or decrease in androgens. Deficient androgens can cause male newborns to be born with external sex organs that are not clearly male or female (ambiguous genitalia) and can affect the development of secondary sexual characteristics of both males and females at puberty.
Pregnenolone, several of the intermediate precursors, and one or more of the steroid hormones can be measured by laboratory tests to determine which enzyme is deficient or defective, based upon which products have been produced and how much.
If both 21- and 11-hydroxylase deficiencies have been ruled out (the most common forms of CAH), then analysis of pregnenolone, along with tests for other precursors, may be used to help establish a diagnosis of 3-beta-hydrosteroid dehydrogenase or 17-alpha-hydroxylase deficiency.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.