Different antibodies, different results: in any case the important measurement is the ferroxidase activity of the protein, not its concentration in the serum. If you want to try and resolve the problem by adding another leg to your comparison,
a) you might consider doing ceruloplasmin by determining the oxidase activity (Ravin HA, J Lab Clin Med 1961, 58:161) which is the method given in the older editions of Varley. It’s very simple and works well on Cobas-type equipment. If you look at the later edition of Varley (by which I mean the 1988, 6th edition) you’ll find that the new authors make disparaging comments about this method, but my experience is that is more precise and reproducible than the immunometric methods, with a much better linearity range. I suspect they had got fed up with re-crystallising the para-phenylenediamine substrate (which is quite toxic and still not supplied in sufficient purity ). Another problem is that lyophilised sera have no enzymatic activity by this method, so you have to calibrate with a frozen serum pool.
b) measure serum copper and see which antibody gives the best agreement [serum copper (mg/dl) x 5 = serum CPL (mg/dL), e.g. Serum Cu of 160 is equivalent to a CPL of 32].
Nick Miller,
London
-----Original Message-----
From: "Musk, Sandy" <[log in to unmask]>
Date: Wed, 12 Dec 2001 13:17:06 +0800
To: [log in to unmask]
Subject: Caeruloplasmin. Beckman v Dade Behring
> A small local survey on specific proteins was recently conducted in Western
> Australia.
> The results for caruloplasmin on fresh serum samples show that the results
> by the Beckman Immage were on average 33% higher than on the Dade Behring
> BNII.
> Subsequent investigation using lyophilised QC material only show about a 10%
> difference.
> It is my understanding that both are standardised against the IFCC
> International Protein Standard CRM 470.
> A similar survey conducted in 1996 with Beckman Array and BNA did not show
> this difference.
>
> Has this difference been reported before?
> Any comments would be appreciated.
>
> Mr Sandy Musk
> Senior Scientist in Charge
> Special Chemistry
> Core Clinical Pathology and Biochemistry
> Laboratory Services
> Royal Perth Hospital
> Western Australia
> Phone 08 9224 1186
> fax 08 9224 2491
>
--
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