Calcaneal quantitative ultrasound reference distributions in Tibetan adults aged 50 years and older across five high-altitude communities: A community-based cross-sectional analysis.

OBJECTIVE: Calcaneal quantitative ultrasound (QUS) may support skeletal risk assessment where dual-energy X-ray absorptiometry is unavailable. We described sex-specific QUS distributions in older Tibetan adults and examined associations with age, body size, and community-level altitude. METHODS: This community-based cross-sectional analysis included 445 ethnic Tibetan adults aged ≥50 years from five communities at 3,650-4,797 m. Calcaneal QUS was measured using a GE Lunar Achilles EXPII. Group comparisons used parametric or nonparametric methods as appropriate. Sex-specific multivariable linear models included age, stature, body weight, and community-level altitude, with HC3 robust standard errors, false discovery rate adjustment for altitude coefficients, and leave-one-community-out cross-validation. RESULTS: The analysis included 188 men and 257 postmenopausal women. Mean (SD) values for SI, BUA, and T-score were 92.4 (20.0), 113.8 (13.6) dB/MHz, and -0.45 (1.49), respectively, and median [25th, 75th percentile] SOS was 1559.4 [1532.4, 1583.4] m/s. Age was inversely associated with all four QUS outcomes in both sexes after adjustment for stature, body weight, and community-level altitude (all P < 0.001), with generally stronger associations in women. Adjusted SI decreased by 0.74 units per additional year of age in men and by 1.11 units in women. No altitude association remained statistically significant after false discovery rate correction. In men, BUA showed a nominal inverse association with altitude, decreasing by 0.65 dB/MHz per 100-m increase (95% CI, -1.22 to -0.07; P = 0.027; q = 0.109). Model explanatory and out-of-community predictive performance were modest; leave-one-community-out R² values ranged from -0.19 to -0.03 in men and from 0.07 to 0.17 in women. CONCLUSION: Age and body size were more consistent correlates of calcaneal QUS than altitude. These sample distributions may inform field-based QUS interpretation and future high-altitude studies, but they should not be used as diagnostic thresholds.