Immunology: antiglobulin test: practice question

A Microbiology 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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Microbiology · Immunology: antiglobulin test

Sample item

A newborn of an Rh-negative mother develops jaundice within 24 hours of birth. Which test confirms that the infant's red cells are coated with maternal antibody?

AKleihauer-Betke test counting fetal cells in maternal bloodBDirect antiglobulin (Coombs) test on the infant's red cellsCIndirect antiglobulin test using the infant's serum and donor red cellsDOsmotic fragility test on the infant's red cells

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

The answer and the reasoning

B. Direct antiglobulin (Coombs) test on the infant's red cells

In Rh haemolytic disease, maternal IgG anti-D crosses the placenta and coats Rh-positive fetal red cells. The direct antiglobulin test adds anti-human globulin to washed infant cells, and agglutination shows in vivo sensitisation. The indirect test detects free antibody in serum.

Option by option

A. Kleihauer-Betke test counting fetal cells in maternal blood
Kleihauer-Betke quantifies fetomaternal haemorrhage to size the anti-D dose.
B. Direct antiglobulin (Coombs) test on the infant's red cells (correct)
Correct. Direct testing detects antibody already bound to the infant's cells.
C. Indirect antiglobulin test using the infant's serum and donor red cells
The indirect test detects free serum antibody, not antibody bound to the infant's cells.
D. Osmotic fragility test on the infant's red cells
Osmotic fragility tests membrane defects such as spherocytosis.

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 Microbiology question

What is the answer to this Microbiology question?

The best answer is B, Direct antiglobulin (Coombs) test on the infant's red cells. In Rh haemolytic disease, maternal IgG anti-D crosses the placenta and coats Rh-positive fetal red cells.

Why is "Kleihauer-Betke test counting fetal cells in maternal blood" not the answer?

Kleihauer-Betke quantifies fetomaternal haemorrhage to size the anti-D dose.

Why is "Indirect antiglobulin test using the infant's serum and donor red cel…" not the answer?

The indirect test detects free serum antibody, not antibody bound to the infant's cells.

Why is "Osmotic fragility test on the infant's red cells" not the answer?

Osmotic fragility tests membrane defects such as spherocytosis.

What concept does this question test?

It tests Immunology: antiglobulin test in Microbiology. The direct antiglobulin test adds anti-human globulin to washed infant cells, and agglutination shows in vivo sensitisation. The indirect test detects free antibody in serum.

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 Immunology: antiglobulin test?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology 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.