Urinary NTX results rarely alter the clinical management of patients with osteoporosis in the tertiary hospital

Using natural, stable calcium isotopes of human blood to detect and monitor changes in bone mineral balance

We are exploring variations in the Ca isotope composition of blood and urine as a new tool for early diagnosis and monitoring of changes in bone mineral balance for patients suffering from metabolic bone disease, cancers that originate in or metastasize to bone, and for astronauts who spend time in low gravity environments. Blood samples are often collected instead of, or in addition to, urine in clinical settings, so it is useful to know if variations in the Ca isotope composition of blood carry the same information as variations in urine. We found that the Ca isotope composition of blood shifts in the same direction and to the same magnitude (~2 parts per ten thousand--pptt) as that of urine in response to skeletal unloading during bed rest. However, the Ca isotope composition of blood is lighter than that of urine by 12 ± 2 pptt. This offset between blood and urine may result from Ca isotope fractionation occurring in the kidneys. This is the first study to confirm the suspected offset between the Ca isotope composition of blood and urine in humans, to directly quantify its magnitude, and to establish that either blood or urine can be used to detect and quantify bone loss.

Quantitative heel ultrasonography, 25-hydroxyvitamin D, and urine amino-terminal cross-linking telopeptide of type I collagen in patients with a recent hip fracture

OBJECTIVE

This study examined quantitative heel ultrasonography (QUS), 25-hydroxyvitamin D (25-OHD) levels, and urine amino-terminal cross-linking telopeptide of type I collagen (NTX-I) levels in patients with a recent osteoporotic hip fracture to see whether they were clinically useful.

METHODS

Stiffness index (SI) T scores from QUS, 25-OHD levels, and urine NTX-I levels were obtained in 53 female and 32 male patients with hip fractures. Sixty-five female patients and 5 male patients attending our geriatric clinic were used for comparison.

RESULTS

The SI T scores of the hip fracture patients were less than those of the geriatric clinic patients. The difference was significant in female patients (P= .0001) but not in male patients (P= .1). Serum levels of 25-OHD were less than 28 ng/mL in 50 of 59 patients and less than 5 ng/mL in 2 patients. Levels of urine NTX-I were variable and were not correlated with other parameters.

CONCLUSIONS

Patients who have had a hip fracture have a low SI determined by QUS; this is easy to perform, and it provides a baseline T score from which to assess treatment effects. Most of these patients are vitamin D deficient, and measurement of the 25-OHD level would enable physicians to prescribe an appropriate dose of vitamin D. Urine NTX-I measured shortly after a hip fracture is not clinically helpful.

Utility of biochemical markers of bone turnover and bone mineral density in management of osteoporosis

Biochemical markers of bone turnover (bone-turnover markers) are released during bone formation or resorption and can be measured in blood and/or urine. The concentration of bone-turnover markers in serum or urine reflect bone remodeling activity and can potentially be used as surrogate markers of the rate of bone formation or bone resorption. While the diagnosis of osteoporosis is based on bone mineral density (BMD), the absolute fracture risk for a particular BMD measurement varies several fold depending on age and is also influenced by other clinical risk factors. The measurement of bone-turnover markers may be of additional value to BMD and clinical risk factors in fracture risk assessment by improving the sensitivity and specificity of prediction of future fractures. In clinical practice, bone-turnover markers may help make cost-effective treatment decisions in patients with borderline absolute risk. BMD changes following treatment cannot be detected with confidence for 12-24 months due to measurement imprecision. Bone-turnover markers, which show an early response following treatment, may be useful for monitoring therapy, identifying non-compliance and non-responders, and predicting early response to therapy. This review concludes by identifying the need for internationally agreed-upon standards for bone resorption and formation.

Natural Calcium Isotopic Composition of Urine as a Marker of Bone Mineral Balance

Background: We investigated whether changes in the natural isotopic composition of calcium in human urine track changes in net bone mineral balance, as predicted by a model of calcium isotopic behavior in vertebrates. If so, isotopic analysis of natural urine or blood calcium could be used to monitor short-term changes in bone mineral balance that cannot be detected with other techniques.

Methods: Calcium isotopic compositions are expressed as δ44Ca, or the difference in parts per thousand between the 44Ca/40Ca of a sample and the 44Ca/40Ca of a standard reference material. δ44Ca was measured in urine samples from 10 persons who participated in a study of the effectiveness of countermeasures to bone loss in spaceflight, in which 17 weeks of bed rest was used to induce bone loss. Study participants were assigned to 1 of 3 treatment groups: controls received no treatment, one treatment group received alendronate, and another group performed resistive exercise. Measurements were made on urine samples collected before, at 2 or 3 points during, and after bed rest.

Results: Urine δ44Ca values during bed rest were lower in controls than in individuals treated with alendronate (P <0.05, ANOVA) or exercise (P <0.05), and lower than the control group baseline (P <0.05, t-test). Results were consistent with the model and with biochemical and bone mineral density data.

Conclusion: Results confirm the predicted relationship between bone mineral balance and calcium isotopes, suggesting that calcium isotopic analysis of urine might be refined into a clinical and research tool.