Oren Zinder wrote:-
"The enzymatic creatinine determination seems not to suffer from this
problem, yet it is much more expensive".
It seems to me the important thing is to be using methods that are
accurate, given that we have a choice. If that is the cost of getting an
accurate result, then that is the cost of getting an accurate result.
What is the cost of getting the answer wrong, for this or any other
analyte? Do anyone's accountants factor that one in?
Surely the better method is that which is more accurate, not that where
the results require to be derived by what appears to be no more than an
arithmetical fiddle for a systematic method error which may not be
constant from patient to patient.
Best wishes
David Cook
Dear all,
We use the rate-blanked Jaffe method for creatinine on our automated
(Roche
747) analyzers.
Recently we have been informed by Roche that in order to correct for the
serum matrix error they are altering their calibrator (Cfas) and
subtracting 26.5 umol/L (0.3 mg/dl) from the result of the
determination.
They require us to do the same with our patient samples.
Although this correction is certainly valid in its reasoning, this
mathematical subtraction (no change in reagent or protocol) results in a
substantial change in the creatinine results which we will be reporting,
especially in children where we often have "non-compensated" levels of
creatinine around 35 - 62 umol/L (0.4-0.7 mg/dl).
In addition, since urine does not have the same matrix problem,
calculation
of the CCT using the "compensated" serum creatinine levels results in a
much higher clearance value (dividing by the lower serum values -
sometimes
half of what they used to be).
The enzymatic creatinine determination seems not to suffer from this
problem, yet it is much more expensive.
I would greatly appreciate comments on this problem,
Thanking you all in advance,
Oren Zinder
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