Hypermagnesemia of ionized magnesium in 199 dogs. A hospital population-based study on prevalence, etiology and prognosis with special emphasis on kidney disease and the measurement of total magnesium

Objective: To investigate the prevalence and etiology of an increased concentration of ionized magnesium (iMg) in dogs and to evaluate its prognostic relevance.Materials and methods: From April 2009 to December 2013, serum electrolytes were measured in 9950 dogs using an ion-selective electrode. Inclusion criterion was an iMg concentration >= 0.68 mmol/l, whereby total Mg (tMg), potassium, ionized calcium, and micturition were also evaluated in this retrospective study. In the case of repeated measurements in an animal, only the initial measurement of the increased iMg concentration was considered. According to the etiology, patients were categorized in the diagnostic groups: azotemia, iatrogenic/medication associated, endocrine diseases, tissue damage, and unknown etiology of hypermagnesemia. The survival rate was analyzed and the iMg concentration was compared between the diagnostic groups. The correlation between iMg and tMg was assessed.Results: The prevalence of increased iMg concentration was 2.0% (199/9950). The most prevalent causes were azotemia (80/199; 40%), followed by iatrogenic hypermagnesemia (37/199; 19%), tissue damage (21/199; 11%), and endocrine diseases (12/199; 6%). In 49/199 cases (25%), the etiology of hypermagnesemia was unknown. An additional hypercalcemia was evident in 24/199 dogs (12 %) and 58/199 (29%) dogs displayed hypocalcemia. In 64% of the dogs (51/80) with azotemia, underlying renal disease was present, from which 53% (27/51) exhibited hyperkalemia. Moreover, 37% (19/51) of the animals with renal disease displayed anuria/oliguria, 59% (11/19) of which were hyperkalemic. Overall, 83/199 (42%) of the dogs died, whereby 48/83 (58%) belonged to the azotemia group. The iMg concentration did not differ significantly between the groups (p = 0.15). There was a poor correlation between iMg and tMg (r(s) = 028).Conclusion: An increased iMg concentration is rare and indicative of a severe disease in the majority of cases. Particularly in patients with acute renal disease, hypermagnesemia can be associated with increased mortality. The tMg concentration does not reflect the iMg concentration.