Intradialytic serum phosphate variations are associated with low PTH levels

Background Numerous studies have explored the role of kidney replacement therapy (KRT) in phosphorus (P) control among prevalent hemodialysis (HD) patients. However, whether the reduction of P achieved during KRT affects parathyroid hormone (PTH) levels is still a matter of debate. Methods We conducted a retrospective observational study on the prevalent HD population at the Division of Nephrology, University Hospital of Verona, from January to December 2022. We Included clinically stable adult patients undergoing HD for over 6 months, with multiple recorded visits during the follow-up. Demographic, clinical, laboratory, and medication data were collected. Time-varying variables were updated at each study visit. The primary outcome of interest was PTH levels. The absolute intra-HD change in P (intra-HD triangle P), defined as the difference between pre- and post-HD P levels, served as the main exposure. Multivariable adjusted linear mixed models were used to investigate the relationship between intra-HD triangle P and PTH levels. Results A total of 211 patients contributed to 904 study visits. A significant and positive relationship was observed between intra-HD triangle P and pre-HD P (beta = 0.76, 95% CI 0.75, 0.78, p < 0.001) and urea reduction ratio (beta = 0.38, 95% CI 0.35, 0.41; p < 0.001). An increase in intra-HD triangle P was significantly and independently associated with low PTH levels (beta = - 0.16, 95% CI - 0.30, -0.03; p = 0.020). Conclusions The extent of intra-HD P reduction significantly correlates with low PTH levels. Strategies focused on optimizing or enhancing depurative efficiency in KRT can exert a substantial impact on managing positive phosphorus balance and secondary hyperparathyroidism. The assessment of intra-HD P reduction may play a pivotal role in the management and follow-up of secondary hyperparathyroidism in HD patients.