Upon completion of the Uncertainty Budget it must be assessed for suitability of use. The purpose of this is to ensure that no obvious over, or under, estimation of the uncertainty is present and that the measurement process is fairly represented.
The suitability can be assessed by comparing the results with any reference standard uncertainty available for the assay. Specifically, it should be the case that the locally derived uncertainty budget should not be lower that than quoted for the reference standard.
Ideally a means to compare results across similar laboratories as a proficiency testing exercise would allow assessment of the appropriateness of the budget. In the absence of such a facility, a suitably well experienced scientist in the field can determine whether the assessment is acceptable.
Acceptance criteria are determined on the basis of each individual assay. Performance is ratified and corrective actions and/or further root cause analysis is instigated if necessary.
The biological variability database provided by http://westgard.com/biodatabase1.htm includes values for many of the measurands analysed. Consequently, the performance of the assays with respect to biological variability are quoted when available, but in some cases performance criteria is defined based on the judgement of the local clinical laboratory.
When biological variability is available and deemed appropriate the levels of performance assessed against are:
- Optimum – Imprecision uncertainty < 0.25 x biological variability
- Desirable – Imprecision uncertainty < 0.50 x biological variability
- Minimum – Imprecision uncertainty < 0.75 x biological variability
As with imprecision uncertainty targets the targets applied to the acceptability criteria of laboratory bias will, when available and appropriate, be set according to the biological variability of the assay according to:
- Optimum – laboratory determined bias < 0.125 (Intra individual biological variation2 + Inter individual biological variation2) 1/2
- Desirable – laboratory determined bias < 0.250 (Intra individual biological variation2 + Inter individual biological variation2) 1/2
- Minimum – laboratory determined bias < 0.375 (Intra individual biological variation2 + Inter individual biological variation2) 1/2
When not available, local laboratory acceptability criteria will be set on an individual assay basis.