CLINICAL-EVALUATION OF THE SERUM CROSSLAPS ONE-STEP ELISA, A NEW ASSAY MEASURING THE SERUM CONCENTRATION OF BONE-DERIVED DEGRADATION PRODUCTS OF TYPE-I COLLAGEN C-TELOPEPTIDES

The Serum CrossLaps(TM) One Step ELISA is a sandwich assay using two m onoclonal antibodies specific for a P-aspartate form of the epitope EK AHDGGR derived from the carboxy-terminal telopeptide region of type I collagen alpha(1)-chain. Our objective was to assess the clinical valu e of the Serum CrossLaps assay for monitoring antiresorptive therapy i n osteoporosis treatment. Samples obtained from postmenopausal women t reated with different doses of cyclic or continuous hormone replacemen t therapy (HRT) with an estrogen analog (tibolone) or with a bisphosph onate (ibandronate) were measured in the Serum CrossLaps One Step ELIS A at baseline and at various time points during therapy. The correspon ding urine samples were measured in the urine CrossLaps(TM) ELISA and corrected for creatinine excretion. The serum CrossLaps measurements a nd corresponding urinary CrossLaps measurements were highly correlated (r >0.8 for all studies). The serum and urine CrossLaps measurements showed a significant decrease among the women treated with clinically relevant doses of either of the antiresorptive agents. Furthermore, th e annual percentage change in bone mineral density (BMD) correlated wi th the measured changes in CrossLaps concentration. The serum CrossLap s assay showed a specificity of 83-100% and a sensitivity of 59-83% fo r assessing BMD changes. The corresponding values for the creatinine-c orrected urinary measurements were 83-92% specificity and 68-79% sensi tivity. We conclude that performance of the convenient Serum CrossLaps One Step ELISA is at least equivalent to that of the urine text for f ollow up of antiresorptive treatment in osteoporosis. Further studies are needed to optimize its use in this and other clinical applications .