Many thanks, as always for your wise words Jonathan.

 

I don’t think many would disagree with your comments but sometimes there are few alternatives to pragmatism – especially when some of our methods are not “good science” in the first place. Rocks and hard places come to mind.

 

Thank you for the references.

 

Best wishes

 

Ian

 

From: Jonathan Middle [mailto:[log in to unmask]]
Sent: 09 June 2010 16:17
To: Ian Barlow
Cc: [log in to unmask]
Subject: Re: NEQAS eGFR/creatinines

 

Hi

Whilst 'anchoring' to a more accurate target (which has been properly validated against the reference method), is desirable, accuracy and traceability of results cannot be assured unless the method used is analytcally specific for the measurand.

It is possible for a manufacturer to claim traceability to IDMS for a method's calibrants, but if the method is not analytically specific, results may still be biased, probably in a concentration-dependent way and probably at important clinical decision points if these are at relatively low concentrations where lack of specificity is more of a problem.

Whilst it may be considered by some to be pragmatically necessary to apply adjustment factors to achieve harmonisation of results for clinical decision making, this is not good science.

The solution is only to use methods which have been validated by a split-sample comparison exercise with the reference method, using a panel of unprocessed sera with endogenous creatinine concentrations within the clinically appropriate range.

Here is a link to the JCTLM database for creatinine reference materials:
http://www.bipm.org/jctlm/search.do?sortBy=Analyte_Name&searchString=creatinine&analyteCategory=Metabolites+and+substrates&matrixCategory=Blood+serum&countryCode=&status=P&type=isRM&x=39&y=5

Look also at : http://www.nkdep.nih.gov/labprofessionals/commutabilitystudy.htm for a US commutability study of creatinine reference materials.

Here is a key reference: http://www.ncbi.nlm.nih.gov/pubmed/18605952


Regards

Jonathan Middle
(in a personal capacity)


On Wed, Jun 9, 2010 at 2:32 PM, Ian Barlow <[log in to unmask]> wrote:

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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Departmental email [log in to unmask]

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------ACB discussion List Information-------- This is an open discussion list for the academic and clinical community working in clinical biochemistry. Please note, archived messages are public and can be viewed via the internet. Views expressed are those of the individual and they are responsible for all message content. ACB Web Site http://www.acb.org.uk Green Laboratories Work http://www.laboratorymedicine.nhs.uk List Archives http://www.jiscmail.ac.uk/lists/ACB-CLIN-CHEM-GEN.html List Instructions (How to leave etc.) http://www.jiscmail.ac.uk/