A Comparison of Serum and Urine N-telopeptide Marker

Osteoporosis is the most common metabolic disorder in the United States and it is estimated that approximately 19% of women and 4% of men over the age 50 years have underlying disease. This number is expected to continue to rise. A silent illness at first, once presenting with fractures, it can lead to increased morbidity, mortality, and decreased quality of life. It carries large financial and societal burdens. Direct annual medical costs are estimated to be approximately 17 to 20 billion dollars in the United States alone. Therefore, it is important to accurately identify those at high risk.

The present gold standard to diagnose osteoporosis is the Dual-energy X-ray absorptiometry (DEXA scan) with a diagnosis based on a T-score of -2.5 SD or below in those without history of fragility fracture. However, many individuals fracture despite having normal or only mildly reduced scores. There are also several barriers within the DEXA technology including accessibility, cost, accurate reference ranges for age and demographic groups that result in missing large groups of people at risk for osteoporosis. The Fracture Risk Assessment Tool (FRAX score) is one tool that identifies those at higher risk of fracture that may benefit from therapy. It was designed and released in 2008 and has been a great asset in clinical practice in stratifying risk and guiding management of osteopenic patients. However, FRAX may miss many individuals that may benefit from therapy due to its limited inclusion criteria.

Bone markers have been shown to predict fracture risk in postmenopausal women independent of bone mineral density and may help identify high risk individuals. Amino-terminal cross-linking telopeptides of type I collagen (NTX) reflects osteoclastic bone resorption. NTX can be measured in both the serum and in urine.

The accuracy of the serum NTX is unclear. It may be less sensitive than urine NTX in detecting bone density changes. The urine NTX overcomes circadian rhythm changes to bone density and is less sensitive to dietary collagen intake. At present, urine markers need to be checked as a second void of the day which may be cumbersome for patients. Serum levels drawn with other bone labs would be easier to obtain than second void urine collections. The study team involved with this research would like to evaluate the correlation between serum and urine NTX in patients with osteopenia with no prior history of osteoporotic treatment. If the urine and serum markers are equivalent methods, serum levels would be preferred to identify high risk patients at risk of disease due to ease of collection.