Communicable diseases: shake test: practice question

A PSM 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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PSM · Communicable diseases: shake test

Sample item

A vial of pentavalent vaccine was accidentally kept in a freezer compartment overnight and then thawed. A shake test is done, comparing it with a vial known to be frozen. The vaccine should be discarded if:

AThe sediment in the test vial settles faster than in the control frozen vialBThe sediment settles slower than in the frozen controlCIt looks clear after shakingDThe vial label is intact

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

The answer and the reasoning

A. The sediment in the test vial settles faster than in the control frozen vial

In a shake test, a suspect vial is compared with a deliberately frozen control. If the suspect vial settles at the same rate or faster, freezing has damaged the adsorbed antigen and it should be discarded. Slower sedimentation indicates it is not damaged.

Option by option

A. The sediment in the test vial settles faster than in the control frozen vial (correct)
Correct. Equal or faster settling means the vaccine has been frozen.
B. The sediment settles slower than in the frozen control
Slower settling suggests the vaccine is potent.
C. It looks clear after shaking
Clarity after shaking is not the criterion.
D. The vial label is intact
A label does not indicate cold chain breach.

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 PSM question

What is the answer to this PSM question?

The best answer is A, The sediment in the test vial settles faster than in the control frozen vial. In a shake test, a suspect vial is compared with a deliberately frozen control.

Why is "The sediment settles slower than in the frozen control" not the answer?

Slower settling suggests the vaccine is potent.

Why is "It looks clear after shaking" not the answer?

Clarity after shaking is not the criterion.

Why is "The vial label is intact" not the answer?

A label does not indicate cold chain breach.

What concept does this question test?

It tests Communicable diseases: shake test in PSM. If the suspect vial settles at the same rate or faster, freezing has damaged the adsorbed antigen and it should be discarded. Slower sedimentation indicates it is not damaged.

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 Communicable diseases: shake test?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM 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.