Clinical biochemistry: primary hyperparathyroidism: 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.

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Biochemistry · Clinical biochemistry: primary hyperparathyroidism

Sample item

A 52-year-old woman has recurrent renal stones and constipation. Serum calcium is 11.4 mg/dL, phosphate is low and intact PTH is raised. Which additional finding is most expected?

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

The answer and the reasoning

B. Mild hyperchloraemic metabolic acidosis with a raised chloride-phosphate ratio

PTH inhibits proximal tubular bicarbonate reabsorption and phosphate reabsorption, so primary hyperparathyroidism tends to cause a mild hyperchloraemic acidosis and a raised chloride-to-phosphate ratio. Urinary calcium is usually raised, and alkaline phosphatase is normal or raised when bone disease is present.

Option by option

  • A. Hypochloraemic metabolic alkalosis with hypokalaemia and low urine chloride

    Alkalosis with hypokalaemia suggests vomiting or diuretic use, not excess PTH.

  • B. Mild hyperchloraemic metabolic acidosis with a raised chloride-phosphate ratio (correct)

    Correct. PTH causes bicarbonate wasting, giving hyperchloraemic acidosis.

  • C. Reduced serum alkaline phosphatase reflecting suppressed osteoblast activity

    Alkaline phosphatase is raised, not reduced, when PTH-driven bone turnover is high.

  • D. Low 24-hour urinary calcium excretion with a clearance ratio below 0.01

    Low urinary calcium with a very low clearance ratio suggests familial hypocalciuric hypercalcaemia.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is B, Mild hyperchloraemic metabolic acidosis with a raised chloride-phosphate ratio. PTH inhibits proximal tubular bicarbonate reabsorption and phosphate reabsorption, so primary hyperparathyroidism tends to cause a mild hyperchloraemic acidosis and a raised chloride-to-phosphate ratio.

Why is "Hypochloraemic metabolic alkalosis with hypokalaemia and low urine ch…" not the answer?

Alkalosis with hypokalaemia suggests vomiting or diuretic use, not excess PTH.

Why is "Reduced serum alkaline phosphatase reflecting suppressed osteoblast a…" not the answer?

Alkaline phosphatase is raised, not reduced, when PTH-driven bone turnover is high.

Why is "Low 24-hour urinary calcium excretion with a clearance ratio below 0.…" not the answer?

Low urinary calcium with a very low clearance ratio suggests familial hypocalciuric hypercalcaemia.

What concept does this question test?

It tests Clinical biochemistry: primary hyperparathyroidism in Biochemistry. Urinary calcium is usually raised, and alkaline phosphatase is normal or raised when bone disease is present.

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: primary hyperparathyroidism?

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.