The aims of this study were to evaluate the components of biological variat
ion of the new markers of bone turnover in patients with Paget's bone disea
se and to compare the results,vith data obtained in healthy subjects, Fifte
en patients with Paget's disease in a stable period of the disease and 12 h
ealthy premenopausal women were included for a 1 year follow-up study. With
in- and between-subject biological variation, indices of individuality, and
critical differences were evaluated for the following biochemical markers:
in serum, total (tAP), and hone (bAP) alkaline phosphatases, procollagen t
ype I N-terminal propeptide (PINP) and beta-carboxyterminal telopeptide of
type I collagen (sCTx); in urine, hydroxyproline (Hyp), and amino (NTx) and
beta-carboxyterminal (CTx) telopeptides of collagen type I. Serum markers
of bone turnover showed lower biological variability than urinary markers.
Within-subject biological variation was higher in pagetic patients than in
healthy subjects for all serum markers, In both groups, bAP presented the l
owest within-subject biological variation. In pagetic patients, all markers
presented indices of individuality of < 0.6, indicating their usefulness F
or patient monitoring. Critical differences were lower for serum markers th
an for urinary markers. Among pagetic patients, serum bAP and PINP showed t
he lowest critical differences with values close to 30%, whereas urinary CT
x presented the highest critical differences (near 70%). Conversely, in hea
lthy subjects, tAP was the marker with the lowest critical differences, bei
ng two-fold higher in pagetic patients. This study confirms the lower sensi
tivity of urinary markers to detect significant changes and indicates that
data obtained on biological variations from healthy populations cannot alwa
ys be extrapolated to pathological conditions. In addition, serum bAP and P
INP seem to be the markers that best reflect a significant change in activi
ty of Paget's disease, (Bone 26:571-576; 2000) (C) 2000 by Elsevier Science
Inc. All rights reserved.