Half-life - Dynamic NPU Manual



Half-time (T½)

Definition in words

Time take for the amount (e.g. number, volume, mass, amount-of-substance) to reach the arithmetic mean of its initial and final equilibrium value, assuming a first-order process.

Definition by equation

k= rate coefficient

Systematic terms

Half-life of component B in system 1

Result type

Rational scale
  • Value sets are positive numerical values
  • Algebraic operations are allowed (a=nb; a≠nb)
Numerical values from 0-∞


s (second), min (minute), h (hour), d (day; 24 hours), m (month), etc.


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. doi:10.1039/9781782622451.


Laboratory field


Clinical Chemistry


Example 1
Generic abbreviated
NPU04192 Pt(P)—Iron elimination; half-life(proc.) = ? min
Full result NPU04192 Patient(Plasma)—Iron elimination; half-life(procedure) = 450 minutes
Abbreviated result NPU04192 Pt(P)—Iron elimination; half-life(proc.) = 450 min
Written expression The half-life of iron elimination in Mr. Smith is [450] min. The measurement is performed in plasma according to procedure defined by the laboratory.

Clinical Pharmacology

Example 2
Generic abbreviated
NPU10317 Pt—Paracetamol; half-life = ? min
Full result NPU10317 Patient—Paracetamol; half-life = 45 minutes
Abbreviated result NPU10317 Pt—Paracetamol; half-life = 45 min
Written expression The half-life of paracetamol in Mr. Smith is [45] min.


  • Kind-of-property

    • Nominal kind-of-property

    • Kind-of-quantity

      • Unitary kind-of-quantity

        • Rational unitary kind-of-quantity

          • Half-life


  • 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
1996-01-01 Half-life Term established