Clinical biochemistry: biochemistry of pyloric stenosis: practice question

A Biochemistry 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.

Try it

Biochemistry · Clinical biochemistry: biochemistry of pyloric stenosis

Sample item

A 5-week-old firstborn boy has projectile non-bilious vomiting after every feed and a palpable olive-shaped epigastric mass. Which biochemical profile is expected?

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

The answer and the reasoning

B. Hypochloraemic, hypokalaemic metabolic alkalosis

Repeated loss of gastric hydrochloric acid causes hypochloraemia and metabolic alkalosis. Volume depletion activates aldosterone, and renal potassium loss produces hypokalaemia. Correction needs rehydration with saline and potassium before pyloromyotomy.

Option by option

  • A. Hyponatraemic, hyperkalaemic metabolic acidosis

    Hyponatraemia with hyperkalaemia and acidosis suggests salt-wasting adrenal hyperplasia, which can mimic pyloric stenosis.

  • B. Hypochloraemic, hypokalaemic metabolic alkalosis (correct)

    Correct. Loss of gastric acid gives hypochloraemic hypokalaemic alkalosis.

  • C. High anion gap metabolic acidosis with hypoglycaemia

    A high anion gap acidosis with hypoglycaemia suggests a metabolic disease, not gastric outlet obstruction.

  • D. Hyperchloraemic, hyperkalaemic metabolic acidosis

    Hyperchloraemic acidosis would follow bicarbonate loss, as in diarrhoea.

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.

More Biochemistry questions

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is B, Hypochloraemic, hypokalaemic metabolic alkalosis. Repeated loss of gastric hydrochloric acid causes hypochloraemia and metabolic alkalosis.

Why is "Hyponatraemic, hyperkalaemic metabolic acidosis" not the answer?

Hyponatraemia with hyperkalaemia and acidosis suggests salt-wasting adrenal hyperplasia, which can mimic pyloric stenosis.

Why is "High anion gap metabolic acidosis with hypoglycaemia" not the answer?

A high anion gap acidosis with hypoglycaemia suggests a metabolic disease, not gastric outlet obstruction.

Why is "Hyperchloraemic, hyperkalaemic metabolic acidosis" not the answer?

Hyperchloraemic acidosis would follow bicarbonate loss, as in diarrhoea.

What concept does this question test?

It tests Clinical biochemistry: biochemistry of pyloric stenosis in Biochemistry. Volume depletion activates aldosterone, and renal potassium loss produces hypokalaemia. Correction needs rehydration with saline and potassium before pyloromyotomy.

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 Clinical biochemistry: biochemistry of pyloric stenosis?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.