From our experience (and while I was at Nottingham) it's impossible to
use this strategy to "screen" for vitamin D deficient patients. You will
miss a significant number of patients. Unfortunately the only way to do
this is to measure vitamin D.
I've been told by colleagues in Australia that the major determinant in
whether someone's PTH rises if they are vitamin D deficient is the
amount of dietary calcium (at least in Rats anyway) this would explain
why we see a large proportion of vitamin D deficient patients with
normal PTH.
In addition the effect of vitamin D on bone is only one aspect of its
actions in the body (immune function, etc etc) I think there is doubt at
the moment at what constitutes an adequate vitamin D concentration as I
think the levels we quote are based on its actions on bone.
Cheers
Craig
-----Original Message-----
From: Clinical biochemistry discussion list
[mailto:[log in to unmask]] On Behalf Of Victoria Clough
Sent: 17 March 2008 13:31
To: [log in to unmask]
Subject: Usefulness of PTH in assessing vitamin D status
We have noticed a significant increase in the number of requests we are
receiving for 25OHD and are trying to establish whether it is always
necessary to measure 25OHD itself or if PTH can be used as a first line
test, with 25OHD being measured only if the PTH is raised. I've come
across a couple of papers which recommend the above approach but have
also
read several which suggest that PTH is no substitute for 25OHD as it can
be
normal in vitamin D deficiency and shows poor correlation with 25OHD,
with
the relationship between the 2 analytes varying with age.
It would be useful to know the approach taken by other labs and I'd be
grateful for any references which decisions have been based on.
Thank you
Victoria Clough
Pre-Registration Clinical Biochemist
King George Hospital, Goodmayes
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