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Dear list members,

at the end of this spring our clinical colleagues complained about our low
25OH D vitamin results. As it turned out their patients mainly were
suspected of having osteoporosis or were of the turkish community here.
Approx. 50% of their patients turned out to have low 25OH D levels. The
below normal results were restricted to these particular 2 colleagues after
a long winter...

We started a comparison of various assays...
correlation of various immunoassays without extraction to group mean of
immunoassays 
r2                   0.95      0,85      0,81        0,83
slope              1,02      0,84      1,15        1,1
intercept         -1          7,8       -3,6         -8,2  (nmol/l)

correlation to 25-OH D3 by HPLC (one 125I antibody and one 3H binding
protein assay)
r2                   0.65 and    0,8
slope              1,5   and    2
intercept         -4     and   -10   (nmol/l)      
(sample size approx 30 in each comparison).

is Your experience the same?
Should one use immunoassays to have a measure(?) of 25OH D as an integrated
value of Vitamin D supply or would it be better to quantitate 25OH D3 or
both 25OH D3 and 25OH D2?

Yours sincerely
Dieter Auch


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Dr. Dieter Auch
Gaffkystrasse 11
D-35392 Giessen
GERMANY