Appendix 1.
Scenario 1. Estimation of MU for a glucose measurement procedure ignoring bias uncertainty (artificial data for illustrative purposes).
| Parameter | Data | Calculations | Comment |
|---|---|---|---|
| Measurand | Amount-of-substance concentration of glucose in plasma or serum | ||
| Units | mmol/L | ||
| Procedure | Hexokinase/G-6-P dehydrogenase | ||
| Traceability | Isotope Dilution-Mass Spectrometry method; high purity preparation, NIST SRM 917b | From reagent manufacturer information sheet. | |
| Imprecision | |||
| QC Level 1: | 04/02/07–08/05/07 | Imprecision for intermediate conditions included one batch change of reagent(s) and calibrator, several operator changes, one instrument routine maintenance. | |
| Mean | 4.80 mmol/L | n=317 data points | |
| SD (uImp) | 0.11 mmol/L | ||
| QC level 2: | |||
| Mean | 15.70 mmol/L | 04/02/07–08/05/07 | |
| SD (uImp) | 0.38 mmol/L | n=320 data points | |
| Bias * | Not assessed | EQA program did not indicate bias problem | |
| Measurement | uProc considered = uc | ||
| Uncertainty uProc | |||
| Plasma glucose: | |||
| 4.8 mmol/L | uProc = uImp = 0.11 mmol/L | ||
| 15.7 mmol/L | uProc = uImp = 0.38 mmol/L | ||
| Expanded uncertainty: | k = 2 | Multiplication of uProc by a coverage factor of 2 provides an interval of values that is believed to include the true value with a coverage probability of 95%. | |
| 4.8 mmol/L | U = 0.22 mmol/L | ||
| 15.7 mmol/L | U = 0.76 mmol/L | ||
| Coverage intervals: | For ease of general use by lab staff and for lab ‘handbooks’, data is rounded. | ||
| 5.0–10.0 mmol/L | ± 0.2 mmol/L | ||
| 10.0–20.0 mmol/L | ± 0.8 mmol/L | Coverage probability 95% |
*
Bias was not evaluated or was evaluated and assessed as not significant.