Diagnostic efficacy of serum cross-linked N-telopeptide (NTx) and aminoterminal procollagen extension propeptide (PINP) measurements for identifying elderly women with decreased bone mineral density

Abstract

The purpose of this study was to determine the diagnostic sensitivity, specificity, predictive value and overall efficiency of serum cross-linked N-telopeptides of bone collagen (NTx) and aminoterminal procollagen extension propeptide (PINP) measurements for identifying women with decreased spine, femoral neck and total body bone mineral density (BMD). Serum NTx and PINP levels and dual X-ray absorptiometry were performed on 196 healthy elderly women, aged 60-90 years. Twelve women were classified as having decreased BMD on the basis of regional and total skeletal densitometric values that were 1.5 to 2.5 standard deviations (SD) below the respective, age-stratified means and were compared with184 women with BMD values greater than 1.5 SD below the mean. The results of receiver operating characteristic analysis revealed that a cutoff level of more than 15.0 nmol BCE/L for serum NTx, as measured by the Osteomark assay (Ostex International, Seattle WA USA) was associated with a 100% sensitivity and 70% specificity rate for identifying postmenopausal women with low BMD. The positive likelihood ratio was 3.3 and the negative predictive value was 1.0 using the 15.0 nmol decision level for NTx. The overall diagnostic efficiency of a single NTx measurement for identifying women with low BMD was 89%. A cutoff level of > 45.0 mug/L for PINP as measured by the Orion Diagnostica RIA assay (Espoo, Finland) had a diagnostic sensitivity of 83% and specificity of 64% for identifying women with decreased BMD. The positive likelihood ratio was 2.3, the negative predictive value 0.98 and the overall diagnostic efficiency 73% using the 45.0 mug/L decision level for PINP. These results warrant future studies using larger populations that are inclusive of more women with low bone mineral density.