B-015 Magnesium Fractionation using Ultrafiltration System

Abstract

Abstract Background Total magnesium (tMg) comprises 3 fractions: ionized (iMg), protein-bound (pbMg), and complexed magnesium (cMg). Serum iMg can be measured directly using ion-selective electrode method, but determination of pbMg and cMg has not been addressed. The aim of this study is to examine the efficiency of a newly introduced ultrafiltration system to fractionate tMg and validate proposed its reference intervals for Mg fractions. Methods Leftover whole blood samples were collected from 40 subjects. iMg and tMG were measured in whole blood using Stat Profile Prime® ES, and ultrafiltrate using VITROS 5600 Analyzer, respectively. Serum fractionation was done by ultrafiltration system (Centrifree®, Sigma-Aldrich, MA, USA). pbMg and cMG were calculated by subtracting tMg ultrafiltrate from tMg in whole blood, and subtracting iMg from tMg concentrations in the ultrafiltrate, respectively. Results Reference intervals of iMg, pbMg, and cMg were proposed as mean± 2 SD of 0.93–1.61 mg/dL, 0–0.85 mg/dL, and 0.07–0.57 mg/dl, respectively. iMg, pbMg, and cMg represented 65%, 20%, and 16% of the tMg concentration in normo-magnesemic subjects with slight variation in hypo- and hyper-magnesemic subjects. iMg showed weak positive correlation with tMg, (r = 0.5, 0.03, 0.005), in normo-magnesemic, hypo- and hyper-magnesemic subjects, respectively. iMg showed weak positive correlation with cMg (r = 0.11) and strongly with pbMg (r = 0.41) in hypermagnesemic subjects. iMg was not dependent on protein concentration or pH, however it correlated positively with blood sugar (r = 0.5 and 0.2) and serum creatinine levels (r = 0.3 and 0.5) in hypo- & hyper-magnesemic subjects, respectively. Conclusions The ultrafiltration system was a promising means to assess cMg and pbMg in critical care patients. iMg measurement provides better discrimination in ill patients and was associated with lifestyle factors including alcohol consumption, hypertension and diabetes. Stat Profile Prime® ES point-of-care analyzer provides rapid and precise direct measurement comparable to current tMg standard method. Due to its rapid turnaround time, it can help to efficiently manage workload of high complexity laboratories, and alleviate the burden on the critical care team.