Whatever the lab does to give confidence in its testing and or calibrations which may include:
1. Proficiency testing
2. Analyzing QC data (incl statistical outliers)
3. Replication using different methods
4. Retesting or recalibrating retained samples/items
5. Monitoring measurement processes (aka supervision)
6. Trending calibration data
7. Investigating out-of-tolerance situations
Lots to get your teeth into.