Table 1. ISO 17511:2003 categories for reference systems.
CategoryReference measurement procedurePrimary (pure-substance) reference materialSecondary (value-assigned) reference materialaExamples
1YesYesPossibleElectrolytes, glucose, cortisol
2YesNoPossibleEnzymes
3YesNoNoHemostatic factors
4NoNoYesProteins, tumor markers, HIV
5NoNoNoEpstein-Barr virus, varicella zoster virus
  • a More than 1 secondary reference material, with potentially different properties, may be available for the same measurand.