Two runs, two numbers

A bench tech runs the same glucose Level 2 control twice in one run, same operator, same reagent lot, same analyzer. The first result is 101 mg/dL. The second is 108 mg/dL. The control's assigned target is 100 mg/dL. Both numbers came from identical conditions, yet they differ from each other by 7 mg/dL and from the target by up to 8 mg/dL.

Before reaching for a rule book, the bench question is simple: what kind of difference is this, and does it matter? A difference between repeats describes precision. A difference from the target describes bias. A single pair of numbers cannot answer both questions on its own, and conflating them leads to the wrong corrective action.

Before troubleshooting a QC flag, decide first whether the pattern looks like scatter, a one-time miss, or a consistent offset, because each has a different fix.