The Better Bones Blog

by Dr. Susan Brown, PhD.

How to tell if you are losing bone without a bone density test

While most doctors tend to monitor bone density with the dual-energy x-ray absorptiomentry (DEXA) test, there is another, less expensive test helpful in determining if you are currently losing bone. This test, called the cross-linked N-teleopeptide (or NTx for short), is a simple urine or blood test known as a “marker of bone resorption.” When you lose bone, small fragments of bone protein show up in the urine and blood, and measuring these bone protein fragments gives an indication of rate of bone breakdown. In most cases a high rate of bone breakdown, also known as bone resorption, indicates that there is an ongoing loss of bone mass.

The bone resorption markers most commonly used are the urine NTx osteomark marker and the urine deoxypyridinium cross-links (Dpd). Your physician can order either of these tests. Generally, a score that’s near or even a bit below the premenopausal mean for women, and one near or even a bit below the young adult mean for men, is ideal. In both tests, the higher the number, the greater the likelihood of a more rapid rate of ongoing bone loss. For more details see my articles on bone density testing and bone resorption testing.

 

How accurate is a DEXA bone density test?

Nearly every day I see women and physicians themselves getting very worried when a woman’s bone density tests show even a small 1-2% decline. Women are often told their fracture risk has greatly increased and that they should immediately begin osteoporosis drug therapy. For many women, the growing “osteoporosis fear” is fueled by small reductions in bone density. But what do these small changes really mean, and just how accurate are the DEXA bone density tests anyway?

Thanks to the excellent work of the University of Washington osteoporosis specialist, Dr. Susan Ott, we now know that the common bone density test is rather imprecise and large changes in density are needed to assure that bone loss is indeed occurring, much less significant in nature. A thoughtful scientist, Dr. Ott had 300 patients get two bone density measurements: one when they came into the room, and the second after walking around the room for a while. With this simple experiment she showed that repeat measurements on the same day may show as much as 7% difference in bone mineral density. Breaking down the data she found that while a 4-6% change in bone mineral density indicates a “probably change” it takes more than a 6% change to fully guarantee a statistically significant change in bone density.

The Better Bones perspective on bone density testing: Bone density testing can be useful, especially when spaced over many years, but small changes are not significant and certainly not a basis for beginning bone drug therapy.

 

Reference:

Dr. Susan Ott’s website: http://courses.washington.edu/bonephys/opBMDp.html

 

How many people who fracture a hip are vitamin D deficient?

The recent explosion of research on vitamin D has made most of us aware that adequate vitamin D is essential for bone health. The degree of its importance, however, is underscored by world-wide research suggesting that practically everyone who experiences an osteoporotic (low-trauma) hip fracture has inadequate levels of vitamin D in his or her blood.

In Minnesota, they looked at 82 adult minimal trauma fractures in people ages 52-97. Ninety-seven percent of all 82 fractures were hip fractures. All but two of the hip fracture patients had low vitamin D levels (below 30 ng/mL). In a large British study, vitamin D deficiency was found in 95% of hip fracture patients as were 78% of hip fracture patients in a recent Boston study.

Such findings have led researchers to ask if vitamin D level is not the best predictor of hip fracture risk. Our research at the Center for Better Bones and the Better Bones Foundation would lead us to agree that low vitamin D should indeed be considered as a major, if not the major, risk factor for hip fracture.

 

References:

Gallacher, S.J. et al. 2005. Prevalence of vitamin D deficiency in Scottish adults with non-vertebral fragility fractures. CMRO, 21, 1355-1361.

Glowacki, J. et al. 2006. Importance of vitamin D in the design of hospital hip fracture care pathways. ASBMR Meeting Abstract #T46.

Malavolta, N. et al. 2005. The relationship of vitamin D status to bone mineral density in an Italian population of postmenopausal women. Osteoporos Int, 16, 1691-1697.

Simonelli, C. et al. 2005. Prevalence of vitamin D inadequacy in a minimal trauma fracture population. CMRO, 21, 1069-1074.

 


Consultation Newsletter Quiz Shop