What is the primary purpose of a quality control sample in a clinical chemistry analyzer?

• A. To calibrate the instrument using known standards.
• B. To monitor assay performance and detect deviations in accuracy or precision during testing.
• C. To replace patient results with control values.
• D. To shorten turn-around time.

Answer: (B)

Quality control samples exist to monitor how well the assay is performing during testing, specifically to detect deviations in both accuracy (closeness to the true value) and precision (reproducibility) as the run proceeds. By running a material with a known target value alongside patient samples, the instrument’s results can be checked against predefined acceptable limits. If the control values stay within those limits, you have confidence that the analyzer, reagents, and procedural steps are functioning correctly for that batch. If a control result falls outside the acceptable range, it signals a problem—such as instrument drift, a reagent issue, temperature fluctuations, or operator error—that needs investigation before patient results are reported. Calibrators set the instrument’s response to known concentrations, while quality control ensures ongoing reliability during testing. Quality control is not meant to replace patient results, nor to shorten turnaround time; its purpose is to ensure accuracy and reliability of results.