Serum Magnesium Concentrations in Association with Canine Calcium Metabolic Disorders
ACVIM 2008
P.A. Schenck
Diagnostic Center for Population and Animal Health, Endocrine Diagnostic Section, Michigan State University
Lansing, MI, USA

Parathyroid hormone (PTH) production is influenced by serum ionized magnesium (iMg) concentration, and either a deficiency or excess may suppress PTH production. Cell membrane receptors also may have decreased sensitivity to serum ionized calcium (iCa) in the presence of low serum iMg concentrations. Many dogs with hypoparathyroidism have been shown to have low serum iMg, but iMg concentrations have not been studied in other calcium metabolic disorders. The objective was to determine the serum iMg status in dogs with calcium metabolic disorders. A total of 19,871 canine cases submitted for PTH and iCa measurement were reviewed, and sorted by diagnosis into the following categories: normal, borderline hypercalcemia, secondary hyperparathyroid, primary hyperparathyroid, parathyroid independent hypercalcemia, humoral hypercalcemia of malignancy (with elevated parathyroid hormone related protein; PTHrP), and hypoparathyroid. In addition, those dogs with a history of chronic renal failure but without secondary hyperparathyroidism were identified for comparison to those with secondary hyperparathyroidism. The mean iMg concentration in each group was within the canine reference range (0.41-0.61 mmol/L); however, there were significant differences in the mean values, and the distribution of concentrations was not the same in each group. Hypoparathyroid dogs (n=794) had the lowest mean iMg concentration (0.46 mmol/L), and 32% of hypoparathyroid dogs had an iMg concentration below the reference range. Dogs with elevated PTHrP (n=1170), parathyroid independent hypercalcemia (n=4379), or primary hyperparathyroidism (n=4761) had a significantly higher mean iMg (0.49, 0.50 and 0.51 mmol/L respectively), with 16%, 16%, and 11% below the reference range respectively. Dogs with secondary hyperparathyroidism (n=2112) had significantly higher iMg concentrations (mean 0.53 mmol/L, median 0.51 mmol/L, 15% below the reference range, 20% above the reference range) than the previous groups, but still significantly lower than normal or borderline hypercalcemic dogs. Mean concentrations of iMg were similar in dogs with normal PTH and iCa concentrations (n=2933, mean 0.54 mmol/L), dogs with borderline hypercalcemia (n=1816, mean 0.53 mmol/L), and in those with CRF but not secondary hyperparathyroidism (n=243, mean 0.53 mmol/L). Approximately 9% of dogs with CRF but not secondary hyperparathyroidism had iMg concentrations below the reference range, as compared to 5% of those with borderline hypercalcemia, and 6% of those with normal PTH and iCa. These data suggest that differences in serum iMg concentrations do occur in association with calcium metabolic disorders.

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Patricia Schenck

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