PRRG2 and hyperinsulinemic hypoglycemia, familial, 4: Regarding the ratio of iMg2+ : tMg2+ levels in the blood, a study concerned with determining the prevalence of Mg2+ deficiency in critically ill patients found the presence of hypomagnesaemia (low tMg2+) in 20–51% of cases and reduced iMg2+ levels in 14–66% of cases [45].