Anion gap as a determinant of ionized fraction of divalent cations in hemodialysis patients
Patients with chronic kidney disease often show altered circulating levels of anions that bind to magnesium and calcium, report researchers at the Osaka University Graduate School of Medicine in Japan (Sakaguchi Y et al, Anion Gap as Determinant of Ionized Fraction of Divalent Cations in Hemodialysis Patients.
The study included 118 HD patients and 112 non-HD nephrology patients. The authors found an almost six-fold higher prevalence of hypermagnesemia defined by total magnesium in HD patients than in non-HD patients (69% versus 12%; P<0.001). However, they also noted that the prevalence of hypermagnesemia defined by ionized magnesium was not significantly different between the two groups: 13% versus 18% (P=0.28). 83% of HD-patients with high total magnesium had normal or low ionized magnesium, and the mean ionized fraction of magnesium in HD patients was significantly lower than that in non-HD patients (51% versus 63%; P<0.001). Likewise, the mean ionized fraction of calcium was slightly lower in HD patients than in non-HD patients (55% versus 56%; P<0.001).
In HD patients with a higher adjusted anion gap than non-HD patients, the ionized fractions of magnesium and calcium were inversely associated with the adjusted anion gap.
In HD patients, the anion gap significantly improved predictions of ionized magnesium and calcium.
Equations that incorporate the anion gap provide better predictions of ionized magnesium and calcium in patients on hemodialysis, summarize the authors.
Link to the study: http://cjasn.asnjournals.org/content/13/2/274.abstract