Dear all,
Its not whether patients are inappropriately classified as having CKD that
is important but rather whether they are inappropriately classified as
having/not having CKD because of bias and imprecision issues. False
negatives are probably more dangerous clinically than false positives in
this context and we must not underestimate the touching importance attached
to eGFR in Primary Care.
Using enzymatic assays to produce a target mean (and therefore a target mean
for eGFR) is surely only appropriate if the target mean approximates to the
calibration point of the assay used to establish the validity of the MDRD
equation. Labs who cannot afford to change may well be tempted to fudge
their non-enzymatic assays to agree with the enzymatically derived mean to
avoid the dreaded persistent poor performance letter resulting in a further
drift of eGFR results from reality (not that I think eGFRs were ever valid).
As a compromise many labs now reflex to enzymic creatinine for icteric,
haemolysed or DKA samples and presumably now they will do the same for EQA
samples.
The relevant CPA standards are F1.1 (validated by manufacturer for their
intended use - how many manufacturers claim their method has been validated
for the production of eGFRs), F3.4 (traceability), H1.1 d to g (EQA, dealing
with non-conformaties). It is not the role of CPA to prescribe/proscribe
ways of getting round analytical problems - that's a personal view
Jeff Slater (Consultant Clinical Scientist - thankfully retired)
-----Original Message-----
From: Clinical biochemistry discussion list
[mailto:[log in to unmask]] On Behalf Of Ian Barlow
Sent: 09 June 2010 14:33
To: [log in to unmask]
Subject: Re: NEQAS eGFR/creatinines
Finlay,
Many thanks for that.
In the spirit of Pathology Harmony I propose that all UKNEQAS
registrants, with immediate effect, "anchor" to the enzymatic mean. I am
sure the purists, and perhaps CPA, will definitely not support this but
surely it is a pragmatic solution to a long standing problem?
Any takers?
Ian
-----Original Message-----
From: Clinical biochemistry discussion list
[mailto:[log in to unmask]] On Behalf Of Finlay MacKenzie
Sent: 09 June 2010 14:19
To: [log in to unmask]
Subject: Re: NEQAS eGFR/creatinines
Ian
Thank for acknowledging BQ/UK NEQAS role in all this.
I'm sure everyone who has read my many comments will be aware of
my views.
For those not familiar with recent progress, in the eGFR Scheme the
target value is now the Enzymatic mean [not the ALTM]. This has only
been brought in since May 2010 at Dist 52.
We have validated this target by a variety of Mass Spec methods /
recoveries etc and believe that this value is a very good estimate of
the
'truth'. The 'historical' ALTM from several years ago was indeed
'wrong', but as the proportion of Enzymatic and Compensated users
increase and the proportion of Traditional Jaffe users decrease, the
ALTM will become more valid.
I'm glad it's not just me who is worried about lack of progress in this
area.
Regards
Finlay
From: Ian Barlow <[log in to unmask]>
To: "[log in to unmask]"
<[log in to unmask]>
Date sent: Wed, 9 Jun 2010 11:53:55 +0100
Subject: NEQAS eGFR/creatinines
Send reply to: Ian Barlow <[log in to unmask]>
Dear all,
I have serious concerns about the spread of creatinine/eGFRr results
on the NEQAS scheme.
I know this is nothing new and am aware of NEQAS past efforts to try
and resolve this using slope adjustments - but has that been effective
in any way?
At present our method group is running with a positive bias of around
15-20% against the ALTM - which clearly is unsatisfactory. However,
is
the ALTM the "true" creatinine?
I am not particularly in favour of "adjusting calibration" but
something needs to be done. Is there a WHO material available that
could be used to "anchor" our method/s against? Or even better, is
there a WHO standard available which the manufacturer's could
calibrated all their assays with? (perhaps they are already doing
this?). I am aware that this is a complex issue as many of the picrate
methods are non-linear in any case. However until we can all afford to
run enzymatic assays we have a problem to deal with as many of our
patients are currently getting classified as CKD erroneously.
I am sure NEQAS, and others have views on this but I for one would
appreciate a rapid solution to this unsatisfactory situation.
Regards
Ian
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