Urinary N-telopeptide levels discriminate normal, osteopenic, and osteoporotic bone mineral density

Background: The level of urinary, type I collagen, crosslinked N-telopeptides (NTX) is a new marker of bone resorption. To our knowledge, no population-based studies of older adults have determined whether this measure can identify individuals with osteoporosis. Objectives: To measure the levels of NTX in a cross-sectional study of ambulatory, older, white adults and to evaluate whether this measure of bone resorption could identify individuals with osteoporosis. Patients and Methods: The subjects, aged 50 to 98 years, formed 3 groups: 374 men, 223 women currently using estrogen, and 364 women not currently using estrogen. A standard medical history and validated record of medication use were obtained. Height and weight were measured. Bone mineral density (BMD) was measured at the hip and lumbar spine using dual energy x-ray absorptiometry. The levels of NTX were measured by enzyme-linked immunosorbent assay. Results: Overall, the levels of NTX increased slightly with age in men and in estrogen users and more dramatically in nonestrogen users. In a model adjusted for all major risk factors for osteoporosis, there was a significant decrease in BMD levels by increasing quintiles of NTX levels at the hip and spine in women with and without estrogen use and at the hip in men; Using sex-specific, peak bone mass criteria and age-adjusted analyses, the levels of NTX discriminated between normal (less than or equal to-1.0 SD), osteopenic (>-1.0 and <-2.5 SD), and osteoporotic (greater than or equal to-2.5 SD) BMD levels in all groups except the spine in men. Conclusions: The levels of NTX uniquely discriminated between older adults with normal, osteopenic, or osteoporotic BMD levels. If confirmed, these data suggest that NTX levels could be used to predict current osteoporosis in older men and women.