Specimens: urine or serum
Units of measurement: BCE/L (where BCE = bone collagen equivalent)
Reference: upper limit of normal for young adult
patient's NTx value as percent of normal young adult =
= (patient's NTx value) / (upper limit of normal reference range for young adult) * 100%
change in NTx with therapy =
= ((NTx before therapy) - (NTx after therapy)) / (NTx before therapy) * 100%
General rules:
(1) In most cases of postmenopausal or age-related osteoporosis the levels of NTx are not greatly increased (no more than 2 times the upper limit of a young adult). A higher concentration may indicate either osteomalacia or a more aggressive form of osteoporosis.
(2) If the osteoporosis is due to a correctable cause, then the NTx levels should return to the normal range if it has been successfully treated.
(3) The goal of therapy in age-related or post-menopausal osteoporosis is to reduce the concentration of NTx by 50 to 60% of the pretreatment level within 3-6 months of starting therapy.
Limitations:
• The assay has a relatively large coefficient of variation.
• Bone resorption varies during the day, so a change in the time of specimen collection may reflect physiologic change rather than response to therapy.
