Magnesium is an abundant intracellularcation, and is an activator of a wide variety of enzyme systems. About 1/3 of blood magnesium is bound to albumin, and the remainder circulates as free magnesium ion. Homeostasis is maintained primarily by renal excretion/ reabsorption. Serum magnesium concentrations may not correlate well with total body magnesium.

High serum magnesium concentrations are seen periodically and usually have little clinical significance. They may occur in end-stage renal failure, with hypocalcemia and adrenal insufficiency.

Low serum magnesium concentrations are seen in critical care patients, which may result in cardiac dysfunction; neuromuscular weak-ness; seizures; hypokalemia, hypophosphatemia, hyponatremia and hypocalcemia. In hypomagnesemic tetany (grass tetany) of cattle, the majority of cases also have hypo-calcemia. The diagnosis of grass tetany can be differentiated from parturient paresis by finding very low levels of urine magnesium in affected cattle (normal urine Mg ++ is ~ 50 mg/dL). Hypomagnesemia can also occur with chronic nutritional deficiency of magnesium; prolonged anorexia; increased losses from vomiting, diarrhea, renal failure, use of diuretics; and altered distribution from sepsis, infusion of blood products, cathecholamine release; hypoaldosteronism; hyperthyroidism; and imbalances of parathyroid metabolism. Disturbances of magnesium metabolism in cattle (calves & adults) and sheep produce similar clinical syndromes of hypomagnesemic tetany that can occur seasonably and on certain pasture types. Goats also can have hypomagnesemia from grazing on fertilized grass pastures.

References: Rosol and Capen, Clinical Biochemistry of Domestic Animals, 5th edition, Academic Press, San Diego, 1997, pp. 678-687; Norris et al, Am J Vet Res 60: 1159-1163, 1999.

The Department of Transportation and OSHA are increasing regulatory scrutiny of the shipment of biopsy specimens. We need your help to comply with these necessary requirements.

Please make sure that biopsy samples are shipped only in appropriate containers with Biohazard labels, which we provide for you in various sizes. Large masses must be submitted following procedures in the December 1999 Antech News.