While the bone density measurement tells us the mineral content of bone at any given time, these tests do not reveal what is currently happening within bone. For example, your DEXA might say you have low bone density, as compared to the standard young reference range. A single bone density measurement, however, cannot distinguish if you are currently losing bone and thus experiencing on-going bone density reduction.

Urinary markers of bone breakdown (known as markers of bone resorption) are simple urine tests, which can help determine if you are currently losing bone or not. These tests can also indicate if your bone-building program is effective at reducing and normalizing the bone breakdown process.

As bone is broken down certain bone protein by-products are excreted in the urine. Measurement of the amount of these bone breakdown by-products can determine the rate of bone breakdown. A high rate of bone breakdown is strongly suggestive of current, on-going bone loss and a greater risk for osteoporotic fracture. A low rate of bone resorption would be one that is similar to that of the ideal young adult for whom bone breakdown and bone build-up should be in balance. Most on-going bone loss is associated with high bone turnover (high turnover osteoporosis). There is, however, also a situation of "low turnover osteoporosis." Here bone breakdown is low as in healthy young adults, but the rate of new bone formation is even lower.

The two most widely used bone resorption markers are the Deoxypyridinoline Crosslinks (known as Dpd) and the N-telopeptides (known as NTx). Both of these are simple tests done on a second-morning urine sample. Your physician can order either of these tests.
At The Osteoporosis Education Project we use these urine markers of bone resorption, along with the DEXA bone density measurements, to determine the effectiveness of our bone building programs. We look for stabilization or increases in bone density over a two-year period. We test the urine markers of bone resorption at baseline, and after a few months to see if our program is reducing bone breakdown. With both urine tests we look to reduce bone breakdown by at least 30% or to bring the rate of bone breakdown at, or near, the young adult range.

It is never too early or too late to begin building and rebuilding bone and these tests can at times help assure that you are on the right path. Remember, however, that both these urine tests exhibit wide within-subject day-to-day variation. Even with proper collection, shipping and processing there is commonly a 30% day-to-day variation in these urine bone breakdown markers. In our studies we like to see more than a 30% reduction in these markers, or normalization to young adult levels.

For instructions on proper collection and handling of these urine marker of bone resorption tests see Bone Resorption Test: Urine Collection Instructions.