The process of modelling and defining the measurand is one that needs only to be performed once, unless significant change in the nature of the measurand occurs.
Below are suggested categories of variables that may influence the definition of the measurand. Each is a potential source of uncertainty in the final report. However, not all categories are expected to influence all assays. For this reason, the input of a suitably qualified scientist is required firstly to determine whether each variable is applicable to a given assay and secondly to decide whether that variable is necessary to be included in the final definition of the measurand.
All information developed throughout this process must be documented in order to provide evidence of full assessment of the measurand definition. Those categories outlined below are by no means an exhaustive list and if there are other contributors thought to have an impact they must be included.
- Purpose of the examination
- Amount/Concentration/Activity
- Source of sample
- Substance in collection tube?
- Concentration of Collection tube substance
- Manual/Semi Automated/Fully Automated/Observation
- Reagent Specific Considerations
- Temperature
- Incubation Time
- Direct Measurement or Calibrated?
- Units
For a full explanation of the influence each of these categories thought to influence the definition of the measurand please refer to the article published in Pathology in Practise (February 2017), or to the publications section of this website
Pathology Uncertainty 