What this case supports, and what it does not

QC alone does not clear a new lot for patient-sample use. A patient-sample comparison across the clinical range and decision points is the check that catches a matrix-dependent bias, and a specimen-by-specimen check against decision points matters more than a single pooled average. The bounded disposition set, accept, reject, restrict, recalibrate, or escalate, follows the investigation sequence that should run before any of those is chosen.

It does not supply a universal numeric critical difference, rejection limit, or sample size; EP26 states those are calculated per assay from local imprecision and the laboratory's chosen CD basis, and the full statistical worksheet lives in the licensed EP26 implementation guide, which is not reproduced here. The six-specimen comparison shows the logic, but its values are not validated acceptance limits for any specific instrument; apply the assay-specific limits established from local imprecision and the laboratory's chosen critical-difference basis.

What depends on local policy: the numeric CD itself, the required sample size and statistical power for Stage 1, which materials beyond patient specimens are acceptable for a given test, whether an IQCP is in place and what it specifies, the laboratory's specific parallel-testing and inventory window, and the exact escalation and lookback procedure. Confirm all of these against your own laboratory's current procedure and the current CAP checklist edition in force, since checklist requirements are revised on a regular cycle.

When a new lot is due for verification, the question to hold onto is not whether QC passed, it is whether patient-sample results near your decision points agree closely enough with the outgoing lot to trust the change, and whether you could show your work if asked.