Table 15. Trend detection.

Recommended practice	Calculation of the CV from all the IQC values corresponding to the results reported by the patients, excluding major errors (CV operating rules defined by the laboratory). Regular monitoring of the CV (monthly, quarterly) according to the methods (and their robustness). Define CV ranges with arguments (national or international publications). Comparison with peer group CVs as part of the external evaluation of the IQC.
Acceptable practice	Regular monitoring of CVs (quarterly) but risk of greater impact in case of significant CV drift.
Unacceptable practice	Exclude IQC values outside the range without investigation, argumentation, and traceability. Frequency of CV follow-up (higher than quarterly follow-up) not supported by arguments. No definition of acceptable CV ranges. No impact assessment when CV ranges are exceeded.
CV – coefficient of variation. IQC – internal quality control.