[Discordance between spine and hip Bone Mineral Density measurement using DXA in osteoporosis diagnosis: prevalence and risk factors].

Background: Diagnostic discordance for osteoporosis is the presence of different categories of T-scores in 2 skeletal sites of an individual patient, falling into 2 different diagnostic categories identified by the World Health Organization classification.

Aim: To determinate the prevalence and risk factors for T-score discordance between spine and hip measurement sites.

Methods: Demographic data, anthropometric measurements, and risk factors for osteoporosis were derived from a database of 1780 patients referred to the outpatient osteoporosis testing center of the departement of Rheumatology between September 2006 and February 2010. Bone mineral density (BMD) was performed by Dual-energy x-ray absorptiometry (DXA) on L1-L4 lumbar spine and total hips for all cases. Minor discordance was considered when the difference between 2 sites was no more than 1 World Health Organization diagnostic class. Major discordance was present when 1 site is osteoporotic and the other is normal.

Results: In 1780 participants (1606 women and 174 males; mean age, 59.5 ± 14.3 years), concordance of T-scores, minor discordance, and major discordance were seen in 49.4%, 45.7%, and 4.8% of the cases, respectively. In both minor and major discordance BMD was lower in lumbar spine than total hips. In univariate and multivariate logistic regression analysis only menopause was identified as risk factors against T-score discordance with p<0.001 and [OR=5.47; IC: 2.61- 12.79]. The others factors: age, gender, BMI, fracture history, corticotherapy, rheumatoid arthritis, tobacco and diabetes were not associated with the T-score discordance.

Conclusion: Clinicians should expect that at least half of patients tested by DXA will demonstrate T-score discordance between spine and total hip measurement sites. T-score discordance can occur for a variety of reasons related to physiologic and pathologic patient factors as well as the performance or analysis of DXA itself.