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ACB-CLIN-CHEM-GEN  June 2008

ACB-CLIN-CHEM-GEN June 2008

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Subject:

Re: eGFR above 60 ml/min

From:

Graham Jones <[log in to unmask]>

Reply-To:

Graham Jones <[log in to unmask]>

Date:

Wed, 4 Jun 2008 10:45:28 +1000

Content-Type:

text/plain

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text/plain (136 lines)

Dear Joe,

The +/- 30% refered to is the scatter of eGFR results around the line of identity when compared with formal GFR measurements. This parameter, the percent of results within +/- 30% has also been used by Levey in work comparing different methods of estimating GFR (eg Cockcroft and Gault, measured creatinine clearance).

I do however question the process of converting IDMS aligned results back to something else for Cockcroft and Gault calculations. It is true that the creatinine results from an IDMS aligned assay are different to those from non-aligned assays. But the assumption that non-aligned assays are in any way related to each other or to the assay used in 1976 by Cockcroft and Gault or the individual assays used for validation of the C&G formula is also not true (see the different conversion factors used in Finlay McKenzies SAUSAGES project from UKNEQAS). If we each back-convert at our institutions the C&G estimates are unchanged locally but will remain different to each other. Leveys IDMS-related formula conversion paper (Ann Int Med 2006,145:247-54) the use of IDMS-aligned creatinine assay produced C&G results on average 20% higher than the measured GFR. A local unpublished study has not confirmed this difference.

What we do have is an urgent need to sort out drug dosing decisions in the world of aligned creatinine assays and the MDRD formula. When is it OK to use the MDRD, when should be "unconvert" for body surface area, when should we calcuate a cockcroft and gault, when should we use another measurement (Cystatin C or formal GFR). More work to keep us interested!

Regards,

Graham



Graham Jones
Staff Specialist in Chemical Pathology
St Vincent's Hospital, Sydney
Ph: (02) 8382-9160
Fax: (02) 8382-2489

>>> "Indovina, Joe [OCDUS]" <[log in to unmask]> 3/06/2008 11:35:06 pm >>>
Dear Graham

May I ask if you could elaborate on point #2? I am wondering what the error of +/- 30% represents. Would this be a single sCR measurement?

The reason ask is estimating possible error with IDMS creatinine, Cockroft Gault, and dosing calculations. In order for me to determine a dosing calculation, I must first convert the IDMS creatinine back to a non idms creatinine. This converted sCR then is run through C-G and then a dosing equation. 

Thank you in advance for your patience and look forward to your reply

Joe

-----Original Message-----
From: Clinical biochemistry discussion list [mailto:[log in to unmask]]On Behalf Of Graham Jones
Sent: Monday, June 02, 2008 8:48 PM
To: [log in to unmask] 
Subject: Re: eGFR above 60 ml/min

The most recent Australian Position Stateme
Dear Rita and others,

The most recent Australian Position Statement on eGFR reporting makes the recommendation that eGFR be reported up to 90 mL/min/1.73m2 (it was up to 60 in the previous version). This should be done only for IDMS aligned assays using the "175" formula. A number of factors were taken into account when making this recommendation:
1. The lack of "early warning" for results falling down towards 60 mL/min if higher results are not reported numerically. ie 61 and 89 and 150 all give the same "information" if reported as ">60".
2. The data we could access (including local studies) suggested that the error of approximately +/- 30% was no worse in the 60 - 90 range than in the <60 range.
3. While the performance of creatinine assays when measuring in the 60 - 90 umol/L range (required for eGFR in the 60-90 mL/min range) is not fantastic, the error is with acceptable limits.
4. A number of labs were alerady doing the 60 - 90 range without apparent adverse effects. One indeed was reporting all results after careful consultation with their renal physicans.

A key issue is the meaning of a result in the 60 - 90 mL/min range. Classically the "normal range" is often described as >90 mL/min. This does not appear to be the case based on studies such as NHANES III, AusDiab and local pathology database extracts. Thus assistance with interpretation of results in the 60 - 90 range is vital, and age is a key factor. A graph showing this relationship is in the guidelines.

The reference is: Medical Journal of Australia 2007; 187 (8): 459-463
http://www.mja.com.au/public/issues/187_08_151007/mat10525_fm.html 

Regards,

Graham


Graham Jones
Staff Specialist in Chemical Pathology
St Vincent's Hospital, Sydney
Ph: (02) 8382-9160
Fax: (02) 8382-2489

>>> Horváth Andrea <[log in to unmask]> 3/06/2008 2:47 am >>>
Dear Colleagues,

In Hungary we are under increasing pressure from some nephrologists that
we give numeric values for eGFR with the MDRD equation in the 60-90
ml/min range, although our current consensus guideline explicitely
states the 60 ml/min cut off above which we do not give eGFR values just
quote the result as greater than 60 ml/min. Some hospitals use the
quadratic equation for eGFR calculations in the 60-90 ml/min range and
the nephrologists propose that we introduce this practice routinely. A
related recent publication in DM can be found in Nephrol Dial Transplant
(2007) 22: 813-818.

I would like to enquire how colleagues elsewhere and around the globe
deal with similar issues locally?

Thanks and regards,

Rita Horvath
Hungary

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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 
List Archives
http://www.jiscmail.ac.uk/lists/ACB-CLIN-CHEM-GEN.html 
List Instructions (How to leave etc.)
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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
List Archives
http://www.jiscmail.ac.uk/lists/ACB-CLIN-CHEM-GEN.html
List Instructions (How to leave etc.)
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