-----Original Message-----
From: Griffiths Paul (RTF) NHCT
Sent: 11 January 2002 16:19
To: 'dr. C.H.H. Schoenmakers'
Subject: RE: Creatinine clearance test
I looked at this same problem in children back in 1981, using a formulae for
GFR estimation based on height and plasma creatinine. I compared this with
Chromium-51 EDTA clearance in 314 children and with measured creatinine
clearance (using 2 x 3 hour collections and adequate water intake, i.e a 6
hour collection period) in 225 children, aged one month to 17 years. This
showed reasonably close agreement at lower levels of clearance, i.e. less
than 60 ml/min/1.73sq m, but considerable scatter at higher clearance
levels. For example at a height(cm)/creatinine (umol/L) ratio of 1.0 we
found that EDTA clearance could vary from 60 to 160 ml/min.1.73 sq m.
There are clearly problems in achieving accurate urine collections,
precision problems particularly at lower creatinine concentrations (i.e
higher GFRs) and interference from non-creatinine chromogens which all add
to the problem. I would therefore agree that care should be taken in using
such formulae and one should be aware of the limitations of such methods.
Paul Griffiths
-----Original Message-----
From: dr. C.H.H. Schoenmakers [mailto:[log in to unmask]]
Sent: 11 January 2002 14:43
To: [log in to unmask]
Subject: Re: Creatinine clearance test
Dear colleagues,
A year ago we investigated the Cockcroft formula for creatinine
clearance by comparing all our measured clearances of the
previous 2,5 year (n=416) with a calculated Cockcroft result. Our
results are attached to this e-mail as an Excel-sheet of 152064
bytes (I have virus checked it, but one can never be to careful in
this). I think these results prove that the Cockcroft formula can over-
or underestimate the true clearance by a factor of more than two.
Therefore one should be very careful when using a Cockcroft
clearance.
Best regards,
Christian
dr. C.H.H. Schoenmakers, European Clinical Chemist
Department of Clinical Chemistry, Elkerliek Hospital
P.O. box 98, 5700 AB Helmond
The Netherlands
(+)31-492-595555 (tel), (+)31-492-595691 (fax)
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