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PubMed This is a summary of 23 peer-reviewed journal articles Updated
Endocrinology

Understanding Your Test Results: Screening and Genetics

At a Glance

Congenital Adrenal Hyperplasia (CAH) is diagnosed using newborn screening for high 17-OHP levels, ACTH stimulation tests for older patients, and CYP21A2 genetic testing. Second-tier tests like LC-MS/MS are often used to rule out false positives in premature babies.

Confirming a diagnosis of Congenital Adrenal Hyperplasia (CAH) involves a series of steps designed to separate true cases from “false alarms” [1]. Whether you are a parent waiting for follow-up results or an adult seeking answers for long-term symptoms, understanding these tests will help you navigate your conversations with specialists.

Newborn Screening: The First Step

In most regions, every baby receives a “heel prick” test shortly after birth. This screening looks for high levels of 17-hydroxyprogesterone (17-OHP), a hormone that builds up when the 21-hydroxylase enzyme is not working correctly [1][2].

  • The Problem with Prematurity: It is very common for premature or low-birth-weight babies to have a “false positive” result [3]. Their immature adrenal glands may naturally produce more 17-OHP, or the stress of early birth can temporarily spike these levels [4][5].
  • How Doctors Adjust: Screening programs use different “cut-off” values based on a baby’s weight and gestational age to reduce these false alarms [6][7].
  • Second-Tier Testing: If the first screen is high, many labs automatically perform a more precise test called LC-MS/MS (Liquid Chromatography-Tandem Mass Spectrometry) [8][6]. This method is the “gold standard” because it can separate 17-OHP from other similar-looking hormones, providing a much more accurate picture [9][10].

The ACTH Stimulation Test

For older children and adults suspected of having Non-Classic CAH, a simple blood test might not be enough. Instead, doctors use a “stress test” for the adrenal glands called the ACTH Stimulation Test (or Cosyntropin test) [11].

  1. The Injection: You are given a synthetic version of ACTH, the hormone the brain uses to tell the adrenal glands to work [11].
  2. The Measurement: Doctors measure your 17-OHP levels before the injection and again 30 to 60 minutes later [11].
  3. The Diagnosis: If your 17-OHP levels jump significantly (often above 10 ng/mL, though LC-MS/MS labs may use lower thresholds), it confirms the adrenal glands are struggling to process hormones correctly [12][9].

Genetic Testing (CYP21A2)

While hormone levels tell us how the adrenal glands are functioning, genetic testing tells us why. The CYP21A2 gene provides the instructions for the 21-hydroxylase enzyme [13].

Modern labs often use Long-Read Sequencing (LRS) [14]. This is an advanced technology that can read through complex parts of your DNA that older tests might miss [15][16]. Genetic testing is crucial because it can:

  • Confirm a diagnosis when hormone tests are borderline [17].
  • Predict whether a baby is at risk for the severe “salt-wasting” form [17][18].
  • Help family members understand their own risk of being “carriers” [17].

Checklist: What to Look for on Your Lab Report

When you receive your results, look for these specific terms and ask your doctor for the context:

  • 17-OHP Level: Was this done via “Immunoassay” or the more accurate “LC-MS/MS”? [9]
  • 21-deoxycortisol: If this level is elevated, it is a very specific sign that 21-hydroxylase is the issue [19][20].
  • Reference Range: Lab results should be compared against ranges specific to your (or your baby’s) age and the specific method the lab used [9][21].
  • Genotype: Does the report list specific mutations (e.g., V281L, I2 Splice, or Null)? [22][23]

Common questions in this guide

Why might my premature baby have a false positive on the CAH newborn screen?
Premature or low-birth-weight babies have immature adrenal glands that can naturally produce higher levels of 17-OHP, the hormone tested during screening. The stress of an early birth can also cause a temporary spike in these hormone levels, leading to a false alarm.
What does a high 17-OHP level mean?
A high 17-OHP level suggests that the 21-hydroxylase enzyme is not working correctly, causing hormones to build up. To confirm this and rule out a false positive, doctors will often order a more precise second-tier test called LC-MS/MS.
How is Non-Classic CAH diagnosed in adults?
Doctors typically use an ACTH stimulation test to diagnose Non-Classic CAH in adults or older children. This involves injecting a synthetic hormone and measuring if your 17-OHP levels jump significantly afterward, which shows the adrenal glands are struggling.
Why is genetic testing used for CAH?
Genetic testing looks closely at the CYP21A2 gene to find out exactly why the adrenal glands aren't working properly. It helps confirm borderline cases, predicts the risk for severe salt-wasting forms, and identifies if family members are carriers.
What does elevated 21-deoxycortisol mean on my lab report?
If your 21-deoxycortisol level is elevated, it is a very specific sign that an issue with the 21-hydroxylase enzyme is causing the adrenal problem. This marker helps doctors confirm a CAH diagnosis more confidently.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What was the specific 17-OHP level on the newborn screen, and was it adjusted for my baby's birth weight and gestational age?
  2. 2.If the 17-OHP was high, has a second-tier LC-MS/MS test (including 21-deoxycortisol) been performed to rule out a false positive?
  3. 3.For the ACTH stimulation test, what are the specific 17-OHP thresholds your laboratory uses for an LC-MS/MS assay?
  4. 4.Did the genetic testing use Long-Read Sequencing to look for complex changes in the CYP21A2 gene, or just a standard mutation panel?
  5. 5.How do these results help us distinguish between Classic and Non-Classic CAH?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (23)
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    Newborn Screening and Diagnosis of Infants with Congenital Adrenal Hyperplasia.

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    Adrenal adenoma secreting 17-hydroxyprogesterone mimicking non-classical 21-hydroxylase deficiency.

    Woźniak B, Leszczyńska D, Szatko A, et al.

    Frontiers in endocrinology 2024; (15()):1499836 doi:10.3389/fendo.2024.1499836.

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    Neonatal 17-hydroxyprogesterone levels adjusted according to age at sample collection and birthweight improve the efficacy of congenital adrenal hyperplasia newborn screening.

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    Clinical endocrinology 2017; (86(4)):480-487 doi:10.1111/cen.13292.

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    Birth Weight- or Gestational Age-adjusted Second-tier LCMSMS Cutoffs Improve Newborn Screening for CAH in New Zealand.

    de Hora MR, Heather NL, Webster D, et al.

    The Journal of clinical endocrinology and metabolism 2021; (106(9)):e3390-e3399 doi:10.1210/clinem/dgab383.

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    Combined Gestational Age- and Birth Weight-Adjusted Cutoffs for Newborn Screening of Congenital Adrenal Hyperplasia.

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    Implementing steroid profiling by liquid chromatography-tandem mass spectrometry improves newborn screening for congenital adrenal hyperplasia in New Zealand.

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    Serum 21-Deoxycortisol for Diagnosis of Nonclassic Congenital Adrenal Hyperplasia in Women With Androgen Excess.

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    The diagnosis of nonclassic congenital adrenal hyperplasia due to 21-hydroxylase deficiency, based on serum basal or post-ACTH stimulation 17-hydroxyprogesterone, can lead to false-positive diagnosis.

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    The spectrum of CYP21A2 gene mutations in patients with classic salt wasting form of 2l-hydroxylase deficiency in a Chinese cohort.

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This page explains Congenital Adrenal Hyperplasia testing and terminology for educational purposes only. Always consult your endocrinologist or pediatrician for help interpreting your specific lab or genetic results.

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