What is the purpose of a delta check in quality control?

• A. To monitor instrument calibration against a standard curve.
• B. To verify assay linearity across concentrations.
• C. To standardize reference intervals across populations.
• D. To compare current patient results to prior results to detect abrupt, unexplained changes.

Answer: (D)

The idea behind a delta check is to compare a patient’s current test result with their own previous result for the same test. If the difference is larger than what would be expected from the assay’s precision and normal biological variation, the result is flagged for review. This helps catch issues like sample mix-ups, mislabeled specimens, or data entry errors, as well as unexpected clinical changes that deserve investigation. It’s not about instrument calibration against a standard curve, not about proving linearity across concentrations, and not about standardizing reference intervals across populations.