Effect of a magnesium-deficient diet on serum and urine magnesium concentrations in healthy cats

Objective-To evaluate the efficacy of using serum total and ionized magnesi um (Mg) concentrations and urine Mg concentrations to identify Mg deficienc y in cats. Animals-6 healthy castrated male cats. Procedure-A Mg-replete diet was fed for:37 days. followed by a Mg-deficient diet for 37 days. On days 1, 3, and 7 of the last week of each diet, serum ionized and total Mg concentrations were determined; in addition; urine Mg concentration was determined each day of the last week. Serum total and io nized Mg concentrations were compared with urine Mg concentration, amount o f Mg excreted during 24 hours (24-hour urine Mg excretion), ratio of urine Mg concentration to urine creatinine concentration (Umg:Ucr), and urinary f ractional excretion of Mg (FEmg) to determine which variable best predicted Mg status. Results-Cats fed Mg-deficient diets had significantly lower serum total and ionized Mg concentrations and 24-hour urine Mg excretion values, compared with cats fed Mg-replete diets. Serum total Mg concentration was the best p redictor of Mg status. Twenty-four-hour urine Mg excretion was a repeatable , reliable measurement; and had the best correlation with serum total Mg co ncentration. Serum total Mg concentration also correlated with urine Mg con centration, Umg:Ucr, and FEmg. Conclusions and Clinical Relevance-Serum total and ionized Mg concentration s can be used to identify cats with dietary-induced Mg deficiencies. Twenty -four-hour urine Mg excretion and urine Mg concentration correlated best wi th serum total Mg concentration and, therefore, may be the most useful urin e variables for identifying Mg deficiency.