Monitoring individual response to hormone replacement therapy with bone markers

Hormone replacement therapy (HRT) induces a rapid decrease in biochemical m arkers of bone turnover that correlate with a subsequent increase in bone m ineral density (BMD), To determine the utility of bone markers in the manag ement of postmenopausal women receiving HRT, we analyzed the relationship b etween changes In four markers (serum osteocalcin and bone alkaline phospha tase [BAP], serum and urinary C-telopeptide of type I collagen [CTX]) and c hanges in spine BMD in 569 women treated for 2 years with different doses o f a matrix transdermal 17 beta-estradiol patch in two placebo-controlled tr ials. Using a logistic regression model, we found that both the percent cha nge from baseline and the actual value of resorption markers at 3 and 6 mon ths of treatment were predictive of BRID response at 2 years. Comparable re sults were obtained with formation markers at 6 months only. We determined the sensitivity, probably of positive BMD response, and corresponding cutof f value of markers at 3 and 6 months with a specificity set at a level of 0 .90, so that <10% of women classified with markers as responders, i.e,, as having a subsequent increase in BMD at 2 years greater than or equal to 2.2 6%, would he false positive. All markers provided a high probability of pos itive BMD response ranging front 0.82 to 0.91, with a sensitivity higher fo r resorption than for formation markers, and sometimes improved in a model combining the percent change and the actual value of marker under HRT. For example, a decrease in serum CTX greater than or equal to 33% at 3 months o f HRT provided a 68% sensitivity and 87% probability of positive BMD respon se at 2 years For a 90% specificity. At 6 months, a decrease in urinary CTX greater than or equal to 53% provided a 68% sensitivity and 91% probabilit y of a positive BR ID response for a 90% specificity. Half of false-negativ e! cases at 3 months will he correctly identified by a subsequent urinary C TX measurement at 6 months. We conclude that the short-term change in bone markers reflects long-term changes of BMD in postmenopausal women treated w ith HRT, Our data suggest that bone turnover markers can he used to monitor the BMD response to HRT at the individual level. Whether such monitoring c ould improve long-term compliance to HRT should be tested prospectively. (S one 26:553-560; 2000) (C) 2000 by Elsevier Science Inc. Ail rights reserved .