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Resolution 12 of the 21st CGPM (1999)
Version française
Special name for the SI derived unit mole per second, the katal, for the expression of catalytic activity

    The 21st Conférence Générale des Poids et Mesures,


  • the importance for human health and safety of facilitating the use of SI units in the fields of medicine and biochemistry,
  • that a non-SI unit called "unit", symbol U, equal to 1 µmol · min-1, which is not coherent with the SI, has been in widespread use in medicine and biochemistry since 1964 for expressing catalytic activity,
  • that the absence of a special name for the SI coherent derived unit mole per second has led to results of clinical measurements being given in various local units,
  • that the use of SI units in medicine and clinical chemistry is strongly recommended by the international unions in these fields,
  • that the International Federation of Clinical Chemistry and Laboratory Medicine has asked the Consultative Committee for Units to recommend the special name katal, symbol kat, for the SI unit mole per second,
  • that while the proliferation of special names represents a danger for the SI, exceptions are made in matters related to human health and safety (15th General Conference, 1975, Resolutions 8 and 9, 16th General Conference, 1979, Resolution 5),
  • noting that the name katal, symbol kat, has been used for the SI unit mole per second for over thirty years to express catalytic activity,

    decides to adopt the special name katal, symbol kat, for the SI unit mole per second to express catalytic activity, especially in the fields of medicine and biochemistry,

    and recommends that when the katal is used, the measurand be specified by reference to the measurement procedure; the measurement procedure must identify the indicator reaction.

Comptes Rendus de la 21e CGPM (1999), 2001, p.334
Metrologia, 2000, 37(1), 87-98

The reader should note that the official version of this Resolution is the French text.

Other Resolutions of the 21st CGPM (1999)
Resolution 1
Resolution 2
Resolution 3
Resolution 4
Resolution 5
Resolution 6
Resolution 7
Resolution 8
Resolution 9
Resolution 10
Resolution 11
Resolution 12
Resolution 13