Normal pregnancy and antenatal care: alkaline phosphatase: practice question

A OBG 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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OBG · Normal pregnancy and antenatal care: alkaline phosphatase

Sample item

At 30 weeks a healthy woman has serum alkaline phosphatase twice the upper limit of normal, with normal bilirubin, transaminases and bile acids. What is the explanation?

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

The answer and the reasoning

B. Placental isoenzyme of alkaline phosphatase

The placenta produces a heat-stable alkaline phosphatase, so the serum level rises progressively in the second and third trimesters, up to two to four times normal. If other liver tests are normal it needs no investigation. Cholestasis is diagnosed by raised bile acids rather than alkaline phosphatase.

Option by option

  • A. Metabolic bone disease

    Bone disease is unlikely when everything else is normal, and the rise is progressive with gestation.

  • B. Placental isoenzyme of alkaline phosphatase (correct)

    Correct. The placental isoenzyme accounts for the rise.

  • C. Intrahepatic cholestasis of pregnancy

    Cholestasis would raise bile acids and usually cause itching.

  • D. Biliary obstruction by gallstones

    Obstruction would raise bilirubin and the patient would have pain or jaundice.

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 OBG question

What is the answer to this OBG question?

The best answer is B, Placental isoenzyme of alkaline phosphatase. The placenta produces a heat-stable alkaline phosphatase, so the serum level rises progressively in the second and third trimesters, up to two to four times normal.

Why is "Metabolic bone disease" not the answer?

Bone disease is unlikely when everything else is normal, and the rise is progressive with gestation.

Why is "Intrahepatic cholestasis of pregnancy" not the answer?

Cholestasis would raise bile acids and usually cause itching.

Why is "Biliary obstruction by gallstones" not the answer?

Obstruction would raise bilirubin and the patient would have pain or jaundice.

What concept does this question test?

It tests Normal pregnancy and antenatal care: alkaline phosphatase in OBG. If other liver tests are normal it needs no investigation. Cholestasis is diagnosed by raised bile acids rather than alkaline phosphatase.

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 Normal pregnancy and antenatal care: alkaline phosphatase?

Learn management algorithms as steps: PPH, eclampsia, ectopic pregnancy. Then use the flashcards and the other OBG 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.