DePTH: De-emphasize Parathyroid Hormone

Because of the kidneys' major role in vitamin D metabolism, most patients with kidney failure on dialysis have biochemical abnormalities that include vitamin D deficiency and high levels of phosphate, fibroblast growth factor-23 (FGF-23), and parathyroid hormone (PTH). All of these abnormalities are associated with cardiovascular disease, bone disease, and death and are major reasons why nephrologists have treated patients on dialysis with activated vitamin D agents for over 30 years. Current guidelines, however, encourage nephrologists to use high doses of vitamin D in order to lower PTH levels to pre-specified treatment targets. This approach to treatment has not been proven to improve health and survival, and may be associated with several harms, including further increasing levels of FGF-23 (a major cardiovascular risk factor), increasing calcium levels, which may promote vascular calcification, low turnover bone disease, and interruptions in vitamin D treatments.

Administering a low, stable dose of vitamin D may be safer and more effective than the current standard of care. The De-emphasize PTH (DePTH) Study is a pragmatic randomized clinical trial of 90 patients on hemodialysis in Seattle, WA, USA that tests whether a low fixed-dose of oral calcitriol (the active form of vitamin D; study intervention) is more safe, effective, and feasible compared with the current usual care. Participants will be recruited at their hemodialysis treatment centers and randomized in a 1:1 ratio to one of these two treatment strategies and followed over 12 months. Participants randomized to the study intervention will receive a fixed dose of calcitriol 0.5 mcg three times a week at their dialysis treatment sessions regardless of PTH level over the ensuing 12 months. Participants randomized to usual care will maintain the existing approach to treating abnormal mineral metabolism using vitamin D doses titrated to monthly to quarterly measurements of PTH. The outcomes for this trial are a panel of blood-based measurements of bone and vascular health that will be drawn at the same time as the blood work done monthly as part of routine dialysis care.