Blood and immunity: factor XIII: practice question

A Physiology 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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Physiology · Blood and immunity: factor XIII

Sample item

A newborn has prolonged bleeding from the umbilical stump and later a delayed haemorrhage after minor trauma. Platelet count, PT, aPTT and thrombin time are all normal. Which defect is most likely?

AAbsent vitamin K-dependent carboxylation of clotting factorsBFailure to cross-link fibrin because of absent fibrin-stabilising factorCAbsent von Willebrand factor multimersDDeficient platelet glycoprotein Ib receptor

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

The answer and the reasoning

B. Failure to cross-link fibrin because of absent fibrin-stabilising factor

Factor XIII, activated by thrombin and calcium, cross-links fibrin strands into a stable clot. Its deficiency gives normal screening tests but weak clots that bleed late, classically with umbilical stump bleeding. Standard PT and aPTT end at fibrin formation, so they miss the defect.

Option by option

A. Absent vitamin K-dependent carboxylation of clotting factors
Vitamin K deficiency would prolong the PT and often the aPTT.
B. Failure to cross-link fibrin because of absent fibrin-stabilising factor (correct)
Correct. Unstabilised fibrin clots form but break down, and standard tests are normal.
C. Absent von Willebrand factor multimers
Von Willebrand deficiency usually prolongs the aPTT through low factor VIII and the bleeding time.
D. Deficient platelet glycoprotein Ib receptor
Glycoprotein Ib deficiency causes thrombocytopenia with giant platelets and a prolonged bleeding time.

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.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is B, Failure to cross-link fibrin because of absent fibrin-stabilising factor. Factor XIII, activated by thrombin and calcium, cross-links fibrin strands into a stable clot.

Why is "Absent vitamin K-dependent carboxylation of clotting factors" not the answer?

Vitamin K deficiency would prolong the PT and often the aPTT.

Why is "Absent von Willebrand factor multimers" not the answer?

Von Willebrand deficiency usually prolongs the aPTT through low factor VIII and the bleeding time.

Why is "Deficient platelet glycoprotein Ib receptor" not the answer?

Glycoprotein Ib deficiency causes thrombocytopenia with giant platelets and a prolonged bleeding time.

What concept does this question test?

It tests Blood and immunity: factor XIII in Physiology. Its deficiency gives normal screening tests but weak clots that bleed late, classically with umbilical stump bleeding. Standard PT and aPTT end at fibrin formation, so they miss the defect.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Blood and immunity: factor XIII?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.