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Cross-sectionnal studies suggest that high levels of both bone formation and resorption are maintained up to 30 yr after the menopause. This high bone turnover rate has been suggested as a risk factor for fast rate of bone loss in postmenopausal women and for increased risk of hip fracture in the aldedy. The clinical use of bone markers (MK) requires that an individual classified at risk, i.e with high bone turnover, on one occasion would be similarly classified on retesting. The aims of this study were to confirm Iongitudinaly the pattern of changes of bone turnover with age and to analyse the concordance of MK levels between different samples. We studied 336 healthy untreated women, 1-39 yr postmenopsuse (age: 63+8 yr) belonging to the OFELY prospective cohort (1039 randomly selected volunteer women, 30-89 yr of age). For each woman, blood and urine (first void ) samples were collected 3 times over 2 yr. We measured serum intact osteocalcin (OC, ELSA-OST-Nat, CIS-Biointernational), and bone-specific alkaline phosphatase (BAP, OSTASE, Hybritech) as MK of bone formation and urinary excretion of type-I collagen C-telopeptide breakdown products (CTX, Cmsslaps, Osteometer) to assess bone resorption. After the marked increase in bone turnover at the time of menopause (+35-40% for bone formation and +75% for bone resorption), longitudinal analysis confirmed a sustained increase in both bone formation and bone resorption long alter the menopause with, however, a significant decrease of CTX in elderly women more than 25 yr after menopause. The mean 2 yr-within-patient coefficient of variation (CV%) was 14% for OC and BAP and 33% for CTX. At baseline high bone turnover was defined as MK levels above 2 SD (lot OC and BAP) or 3 SD (for CTX) from the mean of premenopausal controls, Le T-score _> 2 and 3 respectively. The table shows the proportion of subjects classified as low and high bone turnover both at baseline and 2 yr later. Due to the within-patient CV of MK, we reasonned that a decrease of 0,5 SD for 0(3 and BAP and 1 SD for CTX would not be significant and thus defined a high bone turnover after 2 yr as a T-score > 1.5 for OC and 8AP and _> 2 for CTX. oc BAP CTX high turnover 11 bale;Ins 32% 28% 2a% % of women with lime classification at baseline and 2 yr. High turnover 74 89 62 Low turnover 84 78 86misc|aselfled patients 19% 19% 21% When 2 MK were combined, the rate ot misclassltled patients at ;' yr was much lower, i.e 5.9 to 10% according to the pair of MK. The rate of misclassification between baseline and 2 yr measurements was similar in early postmenopausal women and in elderly. We conclude that biochemical markers have good longterm stability and that a single assessment of 2 MK should correctly classify most of postmenopausal women. PMo426 SMALL ANIMAL APPLICATIONS ON A FAN BEAM BONE DENSITOMETER

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