Magnesium is the fourth most abundant mineral in the body.
Magnesium is absorbed from the diet in the upper intestine, and excreted in the
kidney. The body conserves magnesium by reabsorption by the renal tubules
therefore in magnesium deficiency urine excretion is extremely low. More than
50% of magnesium in the bone, associated with calcium and phosphorus, the
remainder is divided between the muscles and soft tissue. Only 1% of magnesium is
found in the blood. Magnesium is predominately and intracellular cation second only
to potassium.
Magnesium is essential for the activation of adenosine triphosphate (ATP) providing
cell energy, and is an essential co-factor for more than 300 separate enzymes. It is
also important for intracellular synthesis of RNA and DNA.
A “magnesium deficiency tetany” where the serum magnesium is very low but the
serum calcium is normal has been described. The patient responds well to
magnesium administration but not calcium.
High plasma magnesium is usually due to increases in medicinal intake such as
magnesium sulphate therapy, magnesium containing antacids and renal failure.
Low plasma magnesium is due either to low intake as in malabsorption or increased
loss of magnesium; renal tubular loss, dialysis with low magnesium dialysate,
hyperaldosteronism, hyperparathyroidism, diabetes mellitus, alcoholism, diuretic
therapy and aminoglycoside therapy.
Low urine magnesium measurement is used to indicate magnesium deficiency as
low excretion rates occur when the body magnesium stores are low. Also reduced
excretion may occur in severe renal failure.
Increased urine magnesium is seen in generalised renal disease, renal tubular
disease, increased production of aldosterone, hyperparathyroidism, diabetes
mellitus, intensive diuretic therapy, alcoholism and gentomycin treatment.
Lipids/Trace Metals
UMG
Collect 24 hour urine samples on acid
Aliquot sample for UCRN analysis
7 days
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