ACTH (Cosyntropin) Stimulation Test

ACTH Stimulation Test, Cortrosyn Stimulation Test, Synacthen Test

BodyBrainAI Team31 Aug 2023
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The 17-hydroxyprogesterone (17-OHP) blood test is an important screening and diagnostic tool that measures the amount of 17-OHP hormone present in the bloodstream. This steroid hormone is produced by the adrenal glands and gonads. By assessing 17-OHP levels, the test can help identify disorders related to abnormal steroid metabolism and adrenal gland dysfunction.

The 17-OHP test is commonly used to screen newborns for congenital adrenal hyperplasia, monitor adrenal function in those with known conditions, evaluate ambiguous genitalia at birth, investigate precocious puberty, confirm adrenal gland tumors, and assist with infertility testing in women. This article will examine when the 17-OHP test is indicated, how it is performed, what the results reveal, and how to interpret high, low or normal findings.

What is 17-Hydroxyprogesterone?

17-Hydroxyprogesterone is a steroid precursor hormone that plays a key role in the production of other sex steroids like androgens and cortisol. It is synthesized from progesterone by an enzyme called 17α-hydroxylase in the adrenal cortex and gonads.

Levels of 17-OHP are regulated through a process called negative feedback. When cortisol levels are high, this signals to the hypothalamus and pituitary gland to slow production of hormones stimulating 17-OHP synthesis, like adrenocorticotropic hormone (ACTH).

In healthy individuals, 17-OHP circulates at relatively low concentrations which fluctuate throughout the day – typically peaking in the morning and reaching a nadir in the evening. The 17-OHP test measures the exact level of 17-OHP present in the blood at the time of sampling.

What is 17-Hydroxyprogesterone Used For?

There are several key uses and indications for 17-OHP testing:

  • Newborn screening for congenital adrenal hyperplasia (CAH) – This is the most common reason to assess 17-OHP levels. All newborns in the United States are screened by blood test for elevated 17-OHP that could indicate CAH, ideally between 2-5 days after birth.

  • Diagnosing and monitoring congenital adrenal hyperplasia – 17-OHP testing is critical for the initial diagnosis of CAH. Levels are also monitored throughout life in those with CAH to ensure steroid replacement therapy is adequate.

  • Evaluating ambiguous genitalia – 17-OHP testing helps identify the cause of ambiguous genitalia observed at birth, which may stem from abnormal androgen exposure.

  • Investigating precocious puberty – Children with very early onset puberty symptoms may undergo 17-OHP testing to check for potential adrenal tumors triggering early maturation.

  • Confirming adrenal gland tumors – Markedly elevated 17-OHP along with other steroid abnormalities supports diagnosis of an adrenal tumor or carcinoma. Serial measurements assess treatment response.

  • Infertility testing – 17-OHP testing may be used in the workup of female infertility to identify luteal phase defects, polycystic ovarian syndrome, or other conditions.

  • Monitoring steroid replacement – Individuals on glucocorticoid therapy for adrenal insufficiency need periodic 17-OHP checks to confirm adequate dosing.

How is the 17-Hydroxyprogesterone Test Performed?

The 17-OHP test requires a blood sample, most often obtained from a vein in the arm through venipuncture. Blood is typically collected in the morning before 10am when 17-OHP levels are highest, creating optimal conditions for analysis.

During the neonatal period, samples for congenital adrenal hyperplasia screening are obtained by pricking the heel of the newborn baby and collecting drops of blood on specialized filter paper cards.

In the laboratory, the 17-OHP sample is processed using an immunoassay technique. This involves adding antibodies that bind and detect 17-OHP molecules, enabling quantification. Results are usually available within 1-3 days.

What Conditions Does 17-Hydroxyprogesterone Test For?

Specifically, the 17-OHP blood test detects and measures the amount of 17-hydroxyprogesterone present in circulation. By assessing these levels, the test can uncover:

  • Congenital adrenal hyperplasia – CAH refers to a family of genetic disorders involving impaired cortisol synthesis. More than 90% of cases are due to 21-hydroxylase deficiency. This enzyme converts 17-OHP to 11-deoxycortisol. Its impairment leads to 17-OHP accumulation.

  • Adrenal hyperplasia – Enlargement of the adrenal cortex increases 17-OHP production and leads to elevated levels. This accompanies disorders like CAH, Cushing’s disease, and adrenal tumors.

  • Enzyme deficiencies – Deficiencies in enzymes needed for steroid synthesis like 21-hydroxylase, 11β-hydroxylase and 3β-hydroxysteroid dehydrogenase result in 17-OHP buildup.

  • Adrenal tumors – Tumors originating from the adrenal cortex increase 17-OHP production and overwhelm the degradation capacity.

  • Precocious puberty – Very early activation of the gonads due to a central cause leads to increased sex steroid secretion. This includes 17-OHP, which stimulates development of secondary sex characteristics.

Why Do I Need a 17-Hydroxyprogesterone Test?

There are a number of reasons your doctor may order 17-OHP testing:

  • To screen female and male newborns for congenital adrenal hyperplasia, the leading indication

  • If you are known to have congenital adrenal hyperplasia, testing monitors your steroid replacement regimen

  • To evaluate the cause of ambiguous genitalia observed at birth

  • To investigate suspected adrenal tumors based on symptoms like rapid weight gain, fatigue, and hypertension

  • To confirm a diagnosis of precocious puberty and rule out an adrenal or gonadal tumor

  • As part of a fertility workup in women with irregular menstrual cycles or infertility

  • To ensure adequate glucocorticoid dosing if you have primary adrenal insufficiency

The 17-OHP test can uncover the underlying etiology of cortisol deficiency, androgen excess, or sex steroid imbalance when this is unclear based on clinical presentation alone.

What Preparation is Needed for 17-Hydroxyprogesterone Testing?

No special preparation is required before 17-hydroxyprogesterone testing. However, there are some factors that can influence 17-OHP levels, which is important to consider:

  • Timing – 17-OHP levels peak in the early morning, so blood samples are best collected before 10am if possible.

  • Oral contraceptives – Birth control pills containing estrogen can decrease 17-OHP levels.

  • Glucocorticoids – Steroid medications like prednisone reduce endogenous 17-OHP production.

  • Other supplements – Androstenedione, DHEA and certain herbs may artificially increase 17-OHP.

  • Anti-seizure drugs – Medications like phenytoin and phenobarbital stimulate 17-OHP secretion.

Be sure to inform your doctor of any medications, supplements, or hormonal treatments you are using. You may need to discontinue these prior to sample collection if they are likely to interfere with testing.

How Long Does it Take to Get 17-Hydroxyprogesterone Results?

The blood draw itself takes only a few minutes. Sample analysis takes between 1-3 days on average after the blood is sent to the laboratory. The results are reported to your ordering doctor once ready.

For congenital adrenal hyperplasia screening in newborns, the process is accelerated to confirm a diagnosis quickly. Heel prick samples are rushed to a designated lab for same-day analysis in most cases. Results are available within 24 hours so corticosteroid treatment can be initiated promptly if needed.

How Should 17-Hydroxyprogesterone Results Be Interpreted?

When interpreting 17-OHP test results, normal reference ranges vary based on age, sex, and stage of pubertal development. Your doctor will take these factors into account. However, some general guidelines for understanding results are:

  • Normal – A normal 17-OHP level essentially rules out CAH, adrenal hyperplasia, precocious puberty or a steroid-secreting tumor.

  • Mildly elevated – A mildly high result may require repeat testing or monitoring. Causes range from adrenal incidentalomas to enzyme defects with minimal symptoms.

  • Markedly elevated – Significant elevations often indicate nonclassic or classic congenital adrenal hyperplasia. Very high levels can also result from adrenal cancers.

  • Low levels – While not common, a low 17-OHP may indicate adrenal insufficiency or impairment in enzymes needed for synthesis.

Significantly abnormal results will always require close review by your doctor, which may entail more laboratory tests or imaging to confirm a diagnosis. Borderline results may call for follow-up monitoring.

In summary, the 17-hydroxyprogesterone test provides crucial insights into adrenal function and steroid hormone status. It serves an important role in screening programs, diagnosis of conditions like CAH, and ongoing disease monitoring. With sound interpretation along with your clinical picture, 17-OHP testing can guide appropriate treatment to optimize health.

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