# Congenital Adrenal Hyperplasia

> Congenital adrenal hyperplasia for NEET-PG Paediatrics: 21-hydroxylase deficiency, salt-wasting crisis, 17-OHP testing and steroid replacement notes.

- Canonical URL: https://prepelephant.com/topics/neet-pg/paediatrics/congenital-adrenal-hyperplasia
- Exam / course: NEET-PG · Subject: Paediatrics
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Congenital Adrenal Hyperplasia", PrepElephant, https://prepelephant.com/topics/neet-pg/paediatrics/congenital-adrenal-hyperplasia

## Direct answer

Congenital adrenal hyperplasia (CAH) is a group of autosomal recessive defects of adrenal steroidogenesis; 21-hydroxylase deficiency causes about nine in ten cases, blocking cortisol and aldosterone synthesis so that excess ACTH drives the gland and shunts precursors into androgens. A newborn girl presents with ambiguous genitalia — clitoromegaly and labial fusion — while a boy looks normal at birth and returns in the second or third week with a salt-wasting crisis of vomiting, dehydration, hyponatraemia, hyperkalaemia and hypoglycaemia. Diagnosis rests on a raised 17-hydroxyprogesterone, and treatment is lifelong glucocorticoid with mineralocorticoid and salt for salt-wasters.

## What you must remember

- **21-hydroxylase deficiency:** the large majority; low cortisol and aldosterone with high 17-hydroxyprogesterone (the diagnostic marker) and excess androgens; presents as salt-wasting, simple virilising or non-classic disease.
- **Salt-wasting crisis:** at one to three weeks with poor weight gain, vomiting, dehydration, hyponatraemia, hyperkalaemia, hypoglycaemia and acidosis — an emergency needing intravenous saline, glucose and hydrocortisone.
- **Genital findings:** virilised genitalia in affected girls; boys appear normal at birth and later show isosexual precocity with pigmentation and phallic growth.
- **Other enzyme defects:** 11-beta-hydroxylase — virilisation with hypertension; 3-beta-hydroxysteroid dehydrogenase — salt-wasting with undervirilised boys; 17-alpha-hydroxylase — hypertension, hypokalaemia and pubertal failure.
- **Workup of ambiguous genitalia:** karyotype, pelvic and adrenal ultrasound, electrolytes, glucose and 17-hydroxyprogesterone, with ACTH stimulation if baseline is equivocal.
- **Treatment:** hydrocortisone in physiological doses (two- to threefold during illness), fludrocortisone with salt for salt-wasters, monitoring electrolytes, renin, 17-OHP, growth and blood pressure.
- **Screening:** newborn 17-hydroxyprogesterone screening exists in many countries but is not yet universal in India — worth noting for programme questions.

## Common confusion

The classic confusion is 21-hydroxylase versus 11-beta-hydroxylase deficiency: both virilise, but only 11-beta causes hypertension from mineralocorticoid precursor accumulation, while 21-hydroxylase salt-wasters become hypotensive. The second trap is the "normal-looking boy": girls come to diagnosis early through ambiguous genitalia, whereas boys present only at the salt-wasting crisis — any male infant with unexplained vomiting and hyponatraemic hyperkalaemia needs urgent 17-hydroxyprogesterone. Distinguish also from androgen insensitivity and 5-alpha-reductase deficiency, which undervirilise boys rather than virilise girls.

## Exam-focused takeaway

NEET-PG leans on four anchors: the enzyme (21-hydroxylase, commonest), the marker (17-hydroxyprogesterone), the crisis (hyponatraemia with hyperkalaemia and hypoglycaemia in a fortnight-old boy) and the treatment (hydrocortisone plus fludrocortisone with stress dosing). Expect vignettes of ambiguous genitalia in a 46,XX newborn — virilising CAH — and laboratory interpretation pairing low cortisol with high ACTH, high renin and high androgens. The enzyme ladder with blood pressure as the discriminator is a repeated one-liner set, and autosomal recessive inheritance with one-in-four recurrence risk feeds counselling stems.

## Frequently asked questions

### Which enzyme deficiency is commonest?

21-hydroxylase deficiency, causing about 90 per cent of cases; it blocks cortisol and aldosterone synthesis and diverts precursors into androgens.

### Why are girls virilised but boys look normal at birth?

Excess adrenal androgens virilise the developing female external genitalia in utero; male genitalia are already virilised, so nothing changes visibly until later precocity.

### What is the diagnostic marker?

A markedly raised serum 17-hydroxyprogesterone, confirmed on the baseline sample or after ACTH stimulation in borderline cases.

### How is a salt-wasting crisis managed?

Intravenous normal saline with dextrose, hydrocortisone and management of hyperkalaemia, with monitoring for shock, arrhythmia and hypoglycaemia.

### How does 11-beta-hydroxylase deficiency differ?

It also virilises, but accumulating 11-deoxycorticosterone produces hypertension and hypokalaemia rather than salt-wasting — the key discriminator.

### What maintenance treatment is needed?

Lifelong hydrocortisone (with fludrocortisone and salt in salt-wasting forms), increased during illness and monitored clinically and biochemically to avoid over- and under-treatment.