Arbitrary catalytic-activity ( - Dynamic NPU Manual

Arbitrary catalytic-activity (


Definition in words

  1. Arbitrary catalytic-activity of component B in system 1 (Ratio scale)
  2. Arbitrary catalytic-activity of component B in system 1 compared with arbitrary catalytic-activity of component B in a reference system (Ordinal scale)

Note 1:The concept has two definitions.

Note 2: The reference system is defined by the laboratory.

Definition by equation

Note 1: Component B is a catalytic component.

Note 2: kprocedure=an arbitrary determined factor defined by the method procedure used.

Result type

Ordinal scale
  • Value set is ranked accoding to magnitude
  • The value set and the limit of the value set are defined by the laboratory
  • The value set can be either numerical values or words.

Example 1

Value set={none<some<high<very high}

Example 2

Value set={low<normal<high}

Example 3

Value set={0<1<2}

Example 4

Value set={negative<positive}

Example 5

Value set={+<++<+++}

  • Algebraic operations are not allowed (Ref. 2, 1.26)
  • Possible comparison of values (a<b, a=b or a>b).
Rational scale
  • Value sets are positive numerical values
  • Numerical values from 0-∞
  • Algebraic operations are allowed
  • Possible comparison of values (a=nb; a≠nb)


International unit (IU) or procedure defined unit (p.d.u.) (non-SI units)

Special rule(s) in the NPU syntax

Component B is termed according to the International Enzyme Nomenclature (see Medical and metrological vocabulary).

“Procedure” is stated in the specification to the kind-of-property in the NPU definition.

“Procedure” indicates that the measurement procedure must be stated somewhere else than the NPU code and there may be difficulties in comparing values for the same NPU code.

If the ratio scale is attributed to the NPU definition, the unit can be non-SI unit.

If the unit is an International Unit (IU), an international certified reference material (e.g. WHO reference material) is specified in the specification to the kind-of-property.

If there exist no international certified reference material, the laboratory can specify the unit at the placeholder, procedure defined unit.

If ordinal scale is attributed, no unit is stated.


  1. Ferard G, Dybkaer R, Fuentes-Arderiu X. Compendium of Terminology and Nomenclature of Properties in Clinical Laboratory Sciences : Recommendations 2016. 1 ed: Royal Society of Chemistry; 2016. 182 p.
  2. Mesures BIdPe. International Vocabulary of Metrology – Basic and General Concepts and Associated Terms VIM 3rd edition JCGM 200:2012 (JCGM 200:2008 with minor corrections). Bureau International des Poids et Mesures; 2008.

Laboratory field


Clinical Chemistry



Example 1 (ratio)
Generic abbreviated
NPU58186 P—Peptidyl dipeptidase A; °C; proc.) = ? (p.d.u.)
Full result NPU58186 Plasma—Peptidyl dipeptidase A; arbitrary catalytic-activity(37 °C; procedure) = 38 ELISA unit
Abbreviated result NPU58186 P—Peptidyl dipeptidase A; °C; proc.) = 38 ELISA unit
Written expression The arbitrary catalytic-activity of Peptidyl dipeptidase A in Mr Smith’s plasma is [38] ELISA unit. The measurement is performed at 37 °C according to a procedure defined by the laboratory,
Notes “ELISA unit” was chosen by a local laboratory as a proprietary measurement unit and not an accepted international unit.
Example 2 (ordinal)
Generic abbreviated form NPU01143 Lkcs(B)—Alkaline phosphatase; = ?
Full form with a result NPU01143 Leukocytes(Blood)—Alkaline phosphatase; arbitrary catalytic-activity(procedure) = 0
Abbreviated form with a result

NPU01143 Lkcs(B)—Alkaline phosphatase; = 0

Written expression The arbitrary catalytic-activity of alkaline phosphatase in leukocytes of Mr. Smiths blood is [0] compared with arbitrary catalytic-activity of alkaline phosphatase in a reference system. The measurement is performed according to a procedure defined by the laboratory,
  1. The reference system is defined by the laboratory.
  2. “0” is a value according to a value set defined by the laboratory.


NPU database, and


    • Kind-of-property

    • Kind-of-quantity

      • Unitary kind-of-quantity

        • Rational kind-of-quantity

          • arbitrary catalytic-activity

      • Ordinal kind-of-quantity

        • arbitrary catalytic-activity


  • Dybkaer R. Concept system on ‘quantity’: formation and terminology. Accredit Qual Assur. 2013;18(3):253-60.
  • Dybkaer R. ISO terminological analysis of the VIM3 concepts ‘quantity’ and ‘kind-of-quantity’. Metrologia. 2010;47(3):127-34.
Date Term Note Reference
1996-01-01 Arbitrary catalytic-activity Term established. NPU database, and
Date Note Example
2019-06-04 Catalytic component B is an enzyme, defined by the international enzyme nomenclature (, and shall be used for catalytic-activity kinds-of-property. Proteins are defined and termed by UNIPROT ( and should not be used in relation to catalytic-activity kinds-of-property. Though there are overlaps between these two nomenclatures..

The enzyme and protein nomenclatures can have different terms for the same molecule.

  • ABC-type protein transporter (Enzyme nomenclature, identifier EC
  • Alpha-hemolysin (Protein nomenclature, UP identifier P09616).