By Dr. Susan Brown

Bone Health Basics

Bone is composed of a living protein framework upon which mineral crystals are placed. As bone breaks down, bits of this living protein framework appear in the urine or the blood. Tests of bone breakdown, called bone resorption tests, measure the amount of one specific bone protein in the urine or in the blood, and thus gauge the current rate of bone breakdown. Markers of bone breakdown (known as markers of bone resorption) are simple tests that can help determine if you are currently losing bone or not. Such bone breakdown testing 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 or blood. 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, ongoing bone loss and a greater risk for osteoporotic fracture. A low rate of bone resorption is generally thought to suggest that one’s rate of bone loss is that of the ideal young adult. Most ongoing bone loss is associated with high bone turnover. There is, however, also a situation of “low turnover osteoporosis.” Here, bone testing shows that bone breakdown is low similar to that of healthy young adults, but the rate of new bone formation is even lower. 

Two common markers of bone breakdown 

The two most widely used bone resorption markers are the N-Telopeptides test (known as NTx) and the C-terminal cross-linked telopeptide test (known as CTx).  

Urine NTx test for bone breakdown: This simple urine test looks at the number of cross-linked N-telopeptides of bone type I collagen (NTx) in the urine.  

It’s never too late 

It is never too early nor too late to begin building and rebuilding bone, and these tests can, at times, help assure that you are on the right path or uncover a hidden cause for ongoing bone loss. Remember, that bone resorption tests exhibit wide within-subject day-to-day variation. Even with proper collection, shipping, and processing, there is a substantial day-to-day variation in these bone breakdown markers. No single test result should be taken as a “bad sign” or an indication that all is not well; instead, the various tests should be used in concert to get an accurate picture of current bone health.