A few participants have shared their Centaur UFC comparison data with me and report similar findings of much higher results.
Looking at the results for the most recent distribution, I see a very mixed picture of 'usual negative' and 'unusual positive' bias - indicating that maybe not all are using the new method yet for UFC. There are only 5 users of the non-extraction method and 2 of the extraction method in the UK, making detailed analysis difficult.
The onus is firmly on Bayer to demonstrate that their procedures for urinary free cortisol are analytically valid. We need to know how they are calibrated and to what standard they are metrologically traceable. Recovery data would also be convincing, as under-recovery was a major problem of the 'old' Centaur assays.
There are a few laboratories in the UK developing tandem mass spectrometry for UFC (although not yet registered for this method in my EQA scheme) who might be able to help out here, but as a guide to 'true' values, the four (non-UK) HPLC users in the UFC scheme and the single (UK) GCMS user, have uniformly around -20% negative bias from the ALTM. Any method producing results strongly positively biased to the ALTM is very likely to be incorrectly calibrated or not adequately specific.
There will be more on this in my Annual Review - currently under construction!
Hope this helps
J
Dr Jonathan Middle
Deputy Director, UK NEQAS Birmingham
0121 414 7300, fax 0121 414 1179
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-----Original Message-----
From: Clinical biochemistry discussion list on behalf of Brian Shine
Sent: Tue 26/09/2006 18:22
To: [log in to unmask]
Subject: Re: Direct Urinary Cortisol using new Bayer kit
We are in a similar fix, and have not been reporting any numbers. We were
getting a bias of about 100 % on extracted urines. At present, we are
reporting any that are below 280 nmol/day as normal, any above 560 as
raised, and scratching our heads about those in between (or sending them
to a lab whose results we think we can believe). In the medium term, I
guess we will look for another immunoassay, but in the long term I think
the only solution is a chromatographic method (there's a nice report in
the Annals this month).
Best wishes,
Brian Shine
> Can anybody using the new Enhanced Bayer cortisol kit for URINARY CORTISOL
> let us know how whether they are reporting patient samples with it. We
> find over recovery by about 300% against the previous kit. We reported
> this to Bayer verbally in June and sent a copy of our comparison in July.
> Bayer were to take it up with the US, but to date no information has been
> received.
> What are the users of the previous Bayer Cortisol kit for urinary Cortisol
> doing, as the old kit is not available. We were aware with problems of
> variable recovery with the old kit. We are not using an extraction method.
> We are in the NEQAS, and Jonathan Middle has recently sent around a
> questionnaire. The DPC and Roche methods listed are both extraction
> methods, so maybe it is naive to hope we could use a direct assay.
> However, the CVs for the three methods listed are pretty poor.
> How have other laboratories solved their problems when urinary Cortisol is
> requested?
> ------------------------------------------------------------------------------------------
>
> Dr Helen Grimes, Dept Clinical Biochemistry, University College Hospital,
> Galway, Ireland
>
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