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PubMed This is a summary of 17 peer-reviewed journal articles Updated
Pediatric Endocrinology · Classic Congenital Adrenal Hyperplasia

Understanding Your Baby's Diagnosis: Classic CAH and the 21-Hydroxylase Enzyme

At a Glance

Classic Congenital Adrenal Hyperplasia (CAH) is a treatable genetic condition where the adrenal glands lack the 21-hydroxylase enzyme. A positive newborn screen requires follow-up tests like a 17-OHP blood test. With daily hormone medication, babies with CAH can live full, healthy lives.

Receiving a phone call about a positive newborn screening result is often a moment of profound shock and anxiety for parents. It is important to remember that the purpose of this screening is to identify babies early so they can receive the care they need to grow up healthy and strong [1][2]. While the term Congenital Adrenal Hyperplasia (CAH) sounds complex, it describes a manageable condition where the body’s “chemical factory” needs a little help to function correctly [3][4].

Understanding the Adrenal Factory

Your baby has two small organs called adrenal glands located on top of the kidneys. These glands are responsible for producing essential hormones that act as messengers, telling the body how to respond to stress and maintain energy [5][6].

In Classic CAH, the adrenal glands are missing a specific tool called the 21-hydroxylase enzyme. Think of this enzyme as a worker on an assembly line. Without enough of this “worker,” the assembly line cannot finish making cortisol (the stress hormone) and often aldosterone (the salt-retaining hormone) [5][7]. Because the line is backed up, the body diverts those materials into making too much of another hormone: androgens (male-type hormones) [8][9].

The Role of Genetics (CYP21A2)

CAH is an autosomal recessive genetic condition [10][11]. This means:

  • The Cause: It is caused by changes (mutations) in the CYP21A2 gene, which provides the instructions for making the 21-hydroxylase enzyme [10][12].
  • The Inheritance: Both parents are typically “carriers” of a mutation. Carriers usually have no symptoms and may not know they carry the gene [10].
  • The Probability: When both parents are carriers, there is a 25% (1 in 4) chance with each pregnancy that the baby will inherit two mutated genes and have CAH [10].

Two Forms of Classic CAH

There are two main types of classic CAH that doctors look for after a positive screen:

  1. Salt-Wasting CAH: This is the most severe form. The body lacks both cortisol and aldosterone. Without aldosterone, the body cannot hold onto salt, which can lead to a “salt-wasting crisis” (dehydration) if not treated promptly [5][13].
  2. Simple-Virilizing CAH: In this form, the body produces enough aldosterone to maintain salt levels but still lacks enough cortisol and produces too many androgens [5][7].

From Screening to Diagnosis

A positive newborn screen is not a final diagnosis; it is a signal to look closer. To confirm the diagnosis, doctors use several tools:

  • 17-OHP Test: They measure the level of 17-hydroxyprogesterone (17-OHP) in the blood. This is the material that “backs up” on the assembly line when the 21-hydroxylase enzyme isn’t working [14][15].
  • Electrolyte Panel: Doctors check sodium and potassium levels to see if the baby is “wasting salt” [14][13].
  • Genetic Testing: They may analyze the CYP21A2 gene to identify the specific mutation, which can help predict the severity of the condition [11][16].

A Path Forward

While the initial news is overwhelming, it is important to know that classic CAH is highly treatable. By providing the body with the hormones it cannot make on its own—typically through daily medication—children with CAH live full, active lives [9][4]. Your medical team, led by a pediatric endocrinologist (a hormone specialist for children), will work closely with you to create a management plan tailored to your baby’s specific needs [2][17].

For more information, please see Symptoms, Subtypes, and the Biology of Classic CAH.

Common questions in this guide

What does a positive newborn screen for CAH mean?
A positive newborn screen is not a final diagnosis, but a signal that more testing is needed. Doctors will use specific blood tests, like the 17-OHP test and an electrolyte panel, to confirm if your baby actually has Congenital Adrenal Hyperplasia.
What is the 17-OHP test?
The 17-OHP test measures the level of 17-hydroxyprogesterone in the blood. This substance builds up in the body when the 21-hydroxylase enzyme isn't working correctly, making it a key tool for diagnosing Classic CAH.
What is the difference between salt-wasting and simple-virilizing CAH?
Salt-wasting CAH is the severe form where the body lacks both cortisol and the salt-retaining hormone aldosterone, risking dangerous dehydration. Simple-virilizing CAH means the body makes enough aldosterone to maintain salt levels safely, but still lacks cortisol.
How is Classic CAH inherited?
CAH is a genetic condition caused by mutations in the CYP21A2 gene. It is inherited in an autosomal recessive pattern, meaning a baby must inherit a mutated gene from both parents, who are usually healthy carriers.
Is Classic Congenital Adrenal Hyperplasia treatable?
Yes, classic CAH is highly treatable. Under the care of a pediatric endocrinologist, children take daily hormone replacement medications to provide the cortisol and aldosterone their bodies cannot make on their own.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Based on my baby's results, does they have the salt-wasting or simple-virilizing form of classic CAH?
  2. 2.What was the 17-OHP level on the screening, and how does it compare to the normal range for their birth weight and age?
  3. 3.What specific mutations were found in the CYP21A2 gene, and what do they tell us about the expected severity?
  4. 4.Is our baby currently at risk for an adrenal crisis, and what are the emergency signs we should watch for right now?
  5. 5.Can you explain the plan for monitoring my baby's electrolytes and hormone levels over the next few weeks?
  6. 6.Who is the pediatric endocrinologist on call that we can reach 24/7 if we have concerns?

Questions For You

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References

References (17)
  1. 1

    Assessment of Long-Read Sequencing-Based Congenital Adrenal Hyperplasia Genotyping Assay for Newborns in Fujian, China.

    Wang X, Lu X, Zheng F, et al.

    International journal of neonatal screening 2025; (11(1)) doi:10.3390/ijns11010022.

    PMID: 40136637
  2. 2

    Review of Health Problems in Adult Patients with Classic Congenital Adrenal Hyperplasia due to 21-Hydroxylase Deficiency.

    Reisch N

    Experimental and clinical endocrinology & diabetes : official journal, German Society of Endocrinology [and] German Diabetes Association 2019; (127(2-03)):171-177 doi:10.1055/a-0820-2085.

    PMID: 30812049
  3. 3

    Genetic and clinical characteristics including occurrence of testicular adrenal rest tumors in Slovak and Slovenian patients with congenital adrenal hyperplasia due to 21-hydroxylase deficiency.

    Saho R, Dolzan V, Zerjav Tansek M, et al.

    Frontiers in endocrinology 2023; (14()):1134133 doi:10.3389/fendo.2023.1134133.

    PMID: 37008950
  4. 4

    [Long-term morbidity in congenital adrenal hyperplasia].

    Tschaidse L, Quitter F, Hübner A, Reisch N

    Der Internist 2022; (63(1)):43-50 doi:10.1007/s00108-021-01223-6.

    PMID: 34978615
  5. 5

    Genetic characterization of a large cohort of Argentine 21-hydroxylase Deficiency.

    Fernández CS, Taboas M, Bruque CD, et al.

    Clinical endocrinology 2020; (93(1)):19-27 doi:10.1111/cen.14190.

    PMID: 32289882
  6. 6

    Adrenal steroidogenesis and congenital adrenal hyperplasia.

    Turcu AF, Auchus RJ

    Endocrinology and metabolism clinics of North America 2015; (44(2)):275-96.

    PMID: 26038201
  7. 7

    Steroid 21-hydroxylase deficiency in congenital adrenal hyperplasia.

    Parsa AA, New MI

    The Journal of steroid biochemistry and molecular biology 2017; (165(Pt A)):2-11 doi:10.1016/j.jsbmb.2016.06.015.

    PMID: 27380651
  8. 8

    Clinical Manifestations and Treatment Challenges in Infants and Children With Classic Congenital Adrenal Hyperplasia Due to 21-Hydroxylase Deficiency.

    Nokoff NJ, Buchanan C, Barker JM

    The Journal of clinical endocrinology and metabolism 2025; (110(Supplement_1)):S13-S24 doi:10.1210/clinem/dgae563.

    PMID: 39836622
  9. 9

    Management of Infants with Congenital Adrenal Hyperplasia.

    Dabas A, Vats P, Sharma R, et al.

    Indian pediatrics 2020; (57(2)):159-164.

    PMID: 32060243
  10. 10

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

    Liu Y, Zheng J, Liu N, et al.

    Molecular genetics & genomic medicine 2020; (8(11)):e1501 doi:10.1002/mgg3.1501.

    PMID: 32959514
  11. 11

    Divergent Gender Identity in a Phenotypic Male with 46XX Karyotype Caused by a Mutation in CYP21A2 Gene with Congenital Adrenal Hyperplasia.

    Kumar KCP, Banik S, Joy P, Sahoo S

    International journal of applied & basic medical research 2024; (14(2)):134-137 doi:10.4103/ijabmr.ijabmr_473_23.

    PMID: 38912360
  12. 12

    Case Report: Infant With Congenital Adrenal Hyperplasia and 47,XXY.

    Song SQ, Gropman A, Benjamin RW, et al.

    Frontiers in genetics 2021; (12()):808006 doi:10.3389/fgene.2021.808006.

    PMID: 35096019
  13. 13

    Congenital adrenal hyperplasia with salt-wasting crisis and arrhythmia: a case study.

    Canlas JF, Ponmani C

    BMJ case reports 2019; (12(1)) doi:10.1136/bcr-2018-227565.

    PMID: 30700462
  14. 14

    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.

    PMID: 39640880
  15. 15

    Issues with the Detection of Large Genomic Rearrangements in Molecular Diagnosis of 21-Hydroxylase Deficiency.

    Concolino P

    Molecular diagnosis & therapy 2019; (23(5)):563-567 doi:10.1007/s40291-019-00415-z.

    PMID: 31317337
  16. 16

    Genetics of 21-hydroxylase deficiency: Clinical presentation should guide the investigation.

    Ilany J

    American journal of medical genetics. Part A 2024; (194(4)):e63513 doi:10.1002/ajmg.a.63513.

    PMID: 38116711
  17. 17

    A Broken Pathway: Understanding Congenital Adrenal Hyperplasia in the Newborn.

    Allis K

    Neonatal network : NN 2021; (40(5)):286-294 doi:10.1891/11-T-694.

    PMID: 34518380

This page explains newborn screening and diagnostic terms for Classic CAH for educational purposes. Always consult your pediatric endocrinologist for specific medical advice, emergency protocols, and treatment plans for your baby.

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