>>We have recently joined 3 laboratories together in a partnership, but we
>>have a problem with units for reporting drugs - both TDM and toxicology.
>>We are reporting molar units in one lab and mass units in the other two,
>>and this has caused a potentially dangerous situation in swapping
>>specimens between laboratories.
I have tried to get some action on this from professional bodies as there are
significant quality and educational issues involved. So far I haven't made
any progress. In the meantime here are some well-rehearsed and conflicting
ideas that crop up early in the numerous debates I've heard.
1 We should immediately abandon decilitres and only use litres in the
denominator. This will remove one source of confusion.
2 We should use gravimetric units as that's how drugs are prescribed.
(Presumably from people who think that numerical compartmental analysis is
widely used by prescribers.)
3 Prescribers hould switch to using molar units in prescriptions in order to
get the right number of molecules of the active substance into the patient.
(Then it wouldn't matter which salt etc is used in the formulation. See also
the wonderful story of the "expert recommendations" in the WHO guidelines for
GTTs and the confusion of glucose and glucose monohydrate, possibly in Keith
Weiner's editorial in the BMJ...)
4 We should use the SI principle of molar units for substances for which we
know the molecular mass.
5 "Molar thinking" improves "chemical pathology thinking"...calculating anion
gaps, why you can omit the concentration of hydrogen ion when calculating
anion gaps (!), explaining "corrected calcium"...
6 For ethanol everyone uses "multiples of the legal limit for driving" when
interpreting reports anyway.
7 Responders to EQAS often make mistakes with the units for assays of
exogenous substances. But that is an artificial situation which may not
represent their own clinical practice.
8 Junior doctors are pretty mobile so local agreements don't solve all the
problems.
9 Much of the interpretation is done in relation to literature values so
local agreements don't solve all the problems.
My own view:
mol/L, and the sooner the better.
Jonathan Kay
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