Effects of adding distal forearm bone densitometry to axial bone densitometry for the diagnosis of osteoporosis: prevalence and risk factors for diagnostic discordance

Introduction: Studies conducted in the past six years, have demonstrated the superiority of distal forearm bone densitometry over axial bone densitometry for the prediction of osteoporotic fractures of the distal radius. However, the addition of distal forearm bone densitometry to axial bone densitometry is not routinely implemented in clinical practice. The aims of this study were to determine the impact of incorporating distal forearm bone densitometry into standard axial bone densitometry on the diagnosis of osteoporosis, to demonstrate the prevalence of discordance in T-score categories (normal, osteopenia, osteoporosis) obtained through various bone densitometry tests, including spine, hip, and distal forearm measurements, and to assess whether age and other potential risk factors can predict major discordance.

Methods: Postmenopausal women aged ≥45 years and men aged ≥50 years who underwent spine, hip, and distal forearm bone densitometry at Prompt Health Center, Faculty of Associated Medical Sciences, Chiang Mai University, Thailand, between January 2021 and December 2021 were recruited. The exclusion criteria were hyperparathyroidism, osteoporosis treatment, and an unknown age at menopause. The T-scores for each skeletal site were categorized as normal, osteopenia, and osteoporosis based on the World Health Organization classification to determine the prevalence of diagnostic discordance. Upstaging of the diagnostic categories from normal or osteopenia to osteoporosis was evaluated by combining distal forearm bone densitometry with axial bone densitometry. Major discordance was defined as having one osteoporotic and one normal T-score. Factors potentially associated with major discordance were explored using univariate and multivariate logistic regression models.

Results: In total, 881 participants (621 women and 260 men; mean age, 59.2 ± 6.7 years) were analyzed. Addition of one-third (1/3) radius bone densitometry to axial bone densitometry resulted in alteration of the diagnosis from normal or osteopenia to osteoporosis in 9.4% participants (10.6% women, 6.5% men). Addition of ultradistal (UD) radius bone densitometry to axial bone densitometry resulted in alteration of the diagnosis from normal or osteopenia to osteoporosis in 17.0% participants (22.1% women, 5.0% men). The rates of major discordance, minor discordance, and concordance between the spine and hip T-scores, between the axial and 1/3 radius T-scores, and between the axial and UD radius T-scores were 1.7%, 35.0%, and 63.3%; 3.2%, 40.5%, and 56.3%; and 1.9%, 40.9%, and 57.2%, respectively. Age >65 years was significantly associated with major spine–hip T-score discordance (adjusted odds ratio [OR], 5.11; 95% confidence interval [CI] = 1.35–19.33; p = 0.016) and major axial–1/3 radius T-score discordance (adjusted OR, 2.7; 95% CI = 1.24–5.87; p = 0.012).

Conclusions: The combination of distal forearm bone densitometry and axial bone densitometry contributes to the identification of more patients with osteoporosis. Diagnostic discordance is observed for at least one-third of the patients who undergo spine, hip, and distal forearm bone densitometry. Age >65 years is a risk factor for major discordance.