CLS Laboratory Quality Control & Assurance 2

Question 1

Two consecutive control results both exceed the same +2SD limit. Which Westgard rule is violated, and what type of error does it suggest?

Accepted Answer

2-2s; systematic error

Answer

The 2-2s rule flags two consecutive results beyond the same 2SD limit, which points to systematic error.

Question 2

In one run, the level 1 control is +2.3SD and the level 2 control is -2.2SD. Which rule is violated?

Accepted Answer

R-4s

Answer

R-4s is violated when the range between two controls in a run exceeds 4SD, and it indicates random error.

Question 3

Ten consecutive control values fall on the same side of the mean but stay within ±2SD. What does this most likely indicate?

Accepted Answer

Systematic shift, such as a calibration change

Answer

The 10x rule detects systematic error, often from a new reagent or calibrator lot or a calibration change.

Question 4

On a Levey-Jennings chart, control values rise steadily over six days in a row. What is the most likely cause?

Accepted Answer

A gradually deteriorating reagent or light source

Answer

A trend is a gradual change in one direction, usually caused by slow deterioration of reagents, a lamp, or an instrument part.

Question 5

A control has a mean of 100 mg/dL and an SD of 4 mg/dL. What is its coefficient of variation?

Accepted Answer

4%

Answer

CV = (SD/mean) × 100 = (4/100) × 100 = 4%.

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