Sakaguchi Y, et al. - Circulating levels of anions that bind to magnesium and calcium are often altered in patients with CKD. However, it is unknown how these alterations affect the ionized fraction of magnesium and calcium. In this current study, it was demonstrated that anions that accumulated in patients on hemodialysis contributed to the lower ionized fraction of magnesium and calcium. In this patient populace, better predictions of ionized magnesium and calcium were afforded by equations that incorporate the anion gap.