What are the causes of hypomagnesemia?
Impact. The impact of hypomagnesemia is underestimated largely because clinicians fail to measure magnesium.12 Since magnesium is a cofactor for more than 300 enzymes and is involved in numerous transport mechanisms, it is not surprising that hypomagnesemia is associated with significant morbidity.
For example, in a study of 381 consecutive admissions at an inner-city hospital,13 approximately half the admissions went to ICUs and half to regular wards. Despite similar Acute Physiology and Chronic Health Evaluator (APACHE) scores at admission, hospital mortality was twice as high for hypomagnesemic patients in both care settings.
TABLE
Causes of hypomagnesemia
| Gastrointestinal |
| Diarrhea, dietary deficiency (including protein-calorie malnutrition, parenteral and enteral feeding with inadequate magnesium, alcoholism, and pregnancy), familial magnesium malabsorption, gastrointestinal fistulas, inflammatory bowel disease, laxative abuse, malabsorption (sprue, steatorrhea, chronic pancreatitis), nasogastric suction, surgical resection, vomiting |
| Renal |
| Alcoholism, diabetes, diuretics (thiazide, loop, and osmotic/hyperglycemia), other medications, hormones (hypoparathyroidism, hyperthyroidism, hyperaldosteronism, SIADH (syndrome of inappropriate antidiuretic hormone secretion), excessive vitamin D, ketoacidosis, renal disease (acute tubular necrosis, interstitial nephritis, glomerulonephritis, post-obstructive diuresis, post-renal transplantation), hypercalcemia/hypophosphatemia, tubular defects (primary magnesium wasting, Welt’s syndrome, Gitelman’s syndrome, renal tubular acidosis) |
| Shifts from extracellular to intracellular fluid |
| Acidosis (correction of), blood transfusions (massive), epinephrine, hungry bone syndrome, insulin/glucose/refeeding syndrome, pancreatitis (acute) |
| Transdermal losses |
| Excessive sweating, massive burns |
Recommendations from others
Several review articles include a comprehensive differential diagnosis for causes of magnesium deficiency based on physiologic principles as listed in the Table, but none provide data on the relative frequency of the various causes in the general population or specific subgroups.6-9
We need to know when magnesium replacement improves patient outcomes
John Hickner, MD, MSc
Department of Family Medicine, The University of Chicago Pritzker School of Medicine, Chicago, Ill
Treating the underlying cause of hypomagnesemia makes sense. However, even though clinicians often treat “the numbers,” it is not clear that magnesium replacement therapy is beneficial in the absence of symptoms caused by the hypomagnesemia. For example, hypomagnesemia is common for patients with acute myocardial infarction, but magnesium replacement therapy has not been shown to improve outcomes in 2 large randomized trials, the Fourth International Study of Infarct Survival (ISIS 4)14 and Magnesium in Coronaries (MAGIC).15 We need better-designed randomized trials to know for what clinical conditions magnesium replacement leads to improved patient-oriented outcomes.
