I agree with Nick Miller's comments about the value of the PPD ferroxidase
assay. Are any UK labs offering this at present? The Wilson's clinic at
the Middlesex (John Walshe, Andrew Lees and myself) has been dependent on
the paraphenylenediamine-Cp offered by Dr Herb Scheinberg at the National
Wilson Disease Center in New York but his lab unfortunately had to close
earlier this year.
I disagree with the formula for relating caeruloplasmin Cp and copper
Cu, 'though (Nick's formula is presumably, (Cp mg/dl)5 = Cu ug/dl):
0.3 % of Cp is Cu, by mass
Non-Cp associated Cu should be ~10 ug/dL or ~1.57 µmol/L or ~10% total
copper,
so
(Cp mg/dl)3 + 10 = Cu µg/dl
i.e. Cu µg/dl - (Cp mg/dl)3 <= 10
or
(Cp mg/L)0.0472 + 1.574 = Cu µmol/L
i.e. Cu µmol/L - (Cp mg/L)0.0472 <= 1.57
This formula holds for PPD-Cp but may give negative results for non-Cp
associated copper where Cp is measured immunologically, presumably because
apoCp bears the same epitope/s as those recognised by some antibodies to
holoCp. This may account for some of the differences encountered in
Western Australia. It certainly causes problems in the biochemical
assessment and monitoring of patients with Wilson's disease when the only
Cp assay available is immunological. A goal for long-term chelation
treatment is to ensure that non-Cp associated Cu remains consistently <10
ug/dl or 1.57 umol/L. However, treated WD patients may have appreciable
circulating apoCp so may have (spuriously) negative non-Cp Cu using this
formula. ApoCp has no ferroxidase activity and negative formula results
rarely occur using the PPD assay.
Godfrey Gillett
----------
From: Nicholas Miller[SMTP:[log in to unmask]]
Reply To: Nicholas Miller
Sent: 12 December 2001 11:57
To: [log in to unmask]
Subject: Re: Caeruloplasmin. Beckman v Dade Behring
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[SMTP:[log in to unmask]]
Reply To: Musk, Sandy
Sent: 12 December 2001 05:17
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 11
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