Sex-specific association between lumbar spine-total hip T-score discordance and all-cause mortality: a prospective cohort study from NHANES.

Abstract

In 6364 US adults aged ≥ 50 with up to 15 years of follow-up, lumbar spine-total hip T-score discordance was associated with all-cause mortality in women but not in men. Total hip T-score was the strongest single-site predictor in both sexes. Lumbar spine bone mineral density may be influenced by degenerative and non-skeletal mineralization in older adults. Whether the discrepancy between lumbar spine and hip T-scores carries prognostic information for mortality remains unclear. We examined the sex-specific association of the lumbar spine-total hip T-score difference (ΔT_LS - TH) with all-cause mortality, alongside site-specific T-scores at the lumbar spine, femoral neck, and total hip. Prospective cohort study of 6364 adults aged ≥ 50 years from five NHANES cycles (2005-2018) linked to the National Death Index through December 31, 2019. Survey-weighted Cox models estimated hazard ratios (HR) for ΔT (LS T-score minus TH T-score), adjusting for age, sex, BMI, eGFR, smoking, and albumin. Sex-specific associations and a sex × ΔT interaction were tested. Candidate joint models were compared to evaluate whether ΔT_LS - TH provided information beyond total hip T-score. Sensitivity analyses included landmark exclusion of early deaths and additional adjustment for baseline comorbidities. Over a median follow-up of 9.3 years, 1155 deaths occurred. A significant sex × ΔT_LS - TH interaction was observed (p = 0.001). In women, ΔT_LS - TH was associated with higher all-cause mortality (HR 1.259 per unit; 95% CI 1.146-1.382; p < 0.001), and comparative models favored ΔT_LS - TH over the conventional lumbar spine-femoral neck difference. In men, the corresponding estimate was smaller and did not meet the conventional threshold for statistical significance (HR 1.084 per unit; 95% CI 0.9998-1.175; exact p = 0.0504). Total hip T-score was the strongest single-site predictor in both sexes (women HR 0.751, p < 0.001; men HR 0.854, p = 0.002). Lumbar spine T-score showed no association with mortality in women after multivariable adjustment. Parallel analyses using raw BMD values supported the same site-specific ranking, with total hip BMD showing the strongest single-site association. In older US adults, the lumbar spine-total hip T-score difference was associated with all-cause mortality in women but not in men, while total hip T-score remained the strongest single-site predictor in both sexes. These findings are consistent with the clinical emphasis on hip measurements when interpreting DXA results in older adults. ΔT_LS - TH may identify a higher-risk pattern of site-specific discordance at the population level, but it should not be used for individual mortality prediction.