Quality control: Westgard rules: 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 · Quality control: Westgard rules

Sample item

A laboratory runs a glucose control with a target mean of 100 mg/dL and a standard deviation of 2 mg/dL. Today the value is 107 mg/dL, the previous two days were within 1 SD. Which rule is violated and what error does it suggest?

A1-2s rule, which requires only a warning and acceptanceB10x rule, suggesting a gradual shiftC1-3s rule, suggesting random error; reject the run and investigateD2-2s rule, suggesting systematic error

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

The answer and the reasoning

C. 1-3s rule, suggesting random error; reject the run and investigate

On a Levey-Jennings chart, a single control more than 3 SD from the mean (here 3.5 SD) violates the 1-3s rule, which is sensitive to random error and also to large systematic error. The run is rejected, patient results are held and the cause is sought. The 1-2s rule is only a warning that prompts inspection of other rules.

Option by option

A. 1-2s rule, which requires only a warning and acceptance
A value beyond 3 SD exceeds the warning level and cannot simply be accepted.
B. 10x rule, suggesting a gradual shift
The 10x rule needs ten consecutive values on one side of the mean.
C. 1-3s rule, suggesting random error; reject the run and investigate (correct)
Correct. One value beyond 3 SD means rejection.
D. 2-2s rule, suggesting systematic error
The 2-2s rule needs two consecutive values beyond 2 SD, which has not occurred.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is C, 1-3s rule, suggesting random error; reject the run and investigate. On a Levey-Jennings chart, a single control more than 3 SD from the mean (here 3.

Why is "1-2s rule, which requires only a warning and acceptance" not the answer?

A value beyond 3 SD exceeds the warning level and cannot simply be accepted.

Why is "10x rule, suggesting a gradual shift" not the answer?

The 10x rule needs ten consecutive values on one side of the mean.

Why is "2-2s rule, suggesting systematic error" not the answer?

The 2-2s rule needs two consecutive values beyond 2 SD, which has not occurred.

What concept does this question test?

It tests Quality control: Westgard rules in Biochemistry. 5 SD) violates the 1-3s rule, which is sensitive to random error and also to large systematic error. The run is rejected, patient results are held and the cause is sought. The 1-2s rule is only a warning that prompts inspection of other rules.

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 Quality control: Westgard rules?

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.