RESUMEN
BACKGROUND: Direct measurements of ionized magnesium (iMg) in serum by ion-selective electrodes have recently become available in clinical practice, and its usefulness needs to be investigated in dialysis patients because chronic renal failure is associated with disturbances in magnesium metabolism. METHODS: We measured serum iMg in 29 hemodialysis (HD) patients and 24 peritoneal dialysis (CAPD) patients using an ion-selective electrode. The results were compared with those from 30 age- matched control patients who were admitted due to non-renal diseases and were confirmed to have normal serum total magnesium (tMg) levels. RESULTS: Serum tMg was significantly higher in both HD (0.95 [0.81-1.06] mmol/L) and CAPD (0.86 [0.74-0.99] mmol/L) patients compared with the controls (0.74 [0.70-0.78] mmol/L). Serum iMg was significantly higher in HD patients (0.65 [0.60-0.72] mmol/L) compared with the controls (0.55 [0.51-0.57] mmol/L), but was not higher in CAPD patients (0.54 [0.50-0.60] mmol/L). Thus, the ionized fraction of serum magnesium (iMg/tMg) was significantly lower in CAPD patients (65.3 [58.8-68.2]%), but not in HD patients (68.7 [63.6-77.0]%), compared with the controls (72.2 [67.2-78.3]%). In dialysis patients, iMg/ tMg was significantly lower in those with residual renal function than in anuric patients (67.5 [63.6-74.8]% vs. 61.4 [56.4-70.7]%). CONCLUSION: In current practice, true hypermagnesemia may exist frequently in HD patients (at predialysis), but not in CAPD patients. The ionized fraction of serum magnesium may be reduced in CAPD patients, but not in HD patients.