Low Time-Weighted Parathyroid Hormone Is Associated with Malnutrition-Inflammation and Functional Dependence in Maintenance Hemodialysis

Background/Objectives: Low parathyroid hormone (PTH) levels in maintenance hemodialysis may reflect malnutrition, inflammation, reduced functional reserve, or low bone turnover rather than optimal CKD-MBD control. We evaluated associations of longitudinal PTH burden with nutritional-inflammatory and functional-dependence profiles, hospitalization, and mortality. Methods: This retrospective cohort included 188 adults receiving maintenance hemodialysis. Serial PTH measurements were summarized using time-weighted mean PTH. Associations with nutritional-inflammatory biomarkers, functional-dependence measures, and hospitalization were assessed using regression models. Mortality was primarily evaluated using a joint longitudinal–survival model linking repeated log2-transformed PTH measurements with time to death and adjusting for age, sex, dialysis vintage, and dialysis access. A 6-month landmark analysis was performed as a complementary sensitivity analysis. Results: Median time-weighted mean PTH was 292 pg/mL. Lower longitudinal PTH burden was associated with lower albumin, cholesterol, and transferrin and higher C-reactive protein and ferritin. Higher PTH was associated with lower odds of worse mobility and dependence in dressing, bathing, toileting, and continence after adjustment. Hospitalization was not significantly associated with PTH. During follow-up, 62 patients died. In the joint model, each twofold higher estimated current PTH level was associated with a lower observed mortality hazard (adjusted hazard ratio [HR] 0.58, 95% confidence interval [CI] 0.46–0.73; p < 0.001). The 6-month landmark analysis included 159 patients and 44 subsequent deaths. Each twofold higher PTH level was associated with lower subsequent mortality hazard (HR 0.69, 95% CI 0.51–0.95; p = 0.021), while PTH < 150 pg/mL was associated with higher mortality than PTH 300–600 pg/mL (HR 2.84, 95% CI 1.22–6.63). Conclusions: Low time-weighted PTH was associated with adverse nutritional-inflammatory and functional profiles, and lower estimated current PTH with higher mortality. Findings were consistent in the 6-month landmark analysis, do not establish causality, and support interpreting PTH in the broader clinical context.