Endocrinology: congenital adrenal hyperplasia: practice question

A General Medicine question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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General Medicine · Endocrinology: congenital adrenal hyperplasia

Sample item

A 10-day-old genetic female infant has ambiguous genitalia, vomiting and dehydration. Serum sodium is 124 mmol/L, potassium 7.0 mmol/L and glucose is low. Which investigation confirms the most likely diagnosis?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Serum 17-hydroxyprogesterone

Classic salt-wasting 21-hydroxylase deficiency causes cortisol and aldosterone deficiency, producing hyponatraemia, hyperkalaemia and hypoglycaemia, and excess androgens that virilise a female foetus. The enzyme block causes accumulation of 17-hydroxyprogesterone, which is markedly raised and used in newborn screening. Treatment is hydrocortisone, fludrocortisone and salt.

Option by option

  • A. Serum aldosterone alone

    Aldosterone is low but not specific, since other causes of salt loss share this.

  • B. Serum testosterone alone

    Testosterone is raised, but this does not identify the enzyme defect.

  • C. Serum 17-hydroxyprogesterone (correct)

    Marked elevation of 17-hydroxyprogesterone confirms 21-hydroxylase deficiency.

  • D. Serum 11-deoxycortisol

    A raised 11-deoxycortisol points to 11-beta-hydroxylase deficiency, which causes hypertension rather than salt loss.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this General Medicine question

What is the answer to this General Medicine question?

The best answer is C, Serum 17-hydroxyprogesterone. Classic salt-wasting 21-hydroxylase deficiency causes cortisol and aldosterone deficiency, producing hyponatraemia, hyperkalaemia and hypoglycaemia, and excess androgens that virilise a female foetus.

Why is "Serum aldosterone alone" not the answer?

Aldosterone is low but not specific, since other causes of salt loss share this.

Why is "Serum testosterone alone" not the answer?

Testosterone is raised, but this does not identify the enzyme defect.

Why is "Serum 11-deoxycortisol" not the answer?

A raised 11-deoxycortisol points to 11-beta-hydroxylase deficiency, which causes hypertension rather than salt loss.

What concept does this question test?

It tests Endocrinology: congenital adrenal hyperplasia in General Medicine. The enzyme block causes accumulation of 17-hydroxyprogesterone, which is markedly raised and used in newborn screening. Treatment is hydrocortisone, fludrocortisone and salt.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Endocrinology: congenital adrenal hyperplasia?

For each disease know the classic presentation, the best test, and the first-line treatment. Then use the flashcards and the other General Medicine questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.