Rational Ordering of Calcium, Magnesium, and Phosphorus in the Emergency Department

Abstract & Commentary

Source: Rose WD, et al. Calcium, magnesium, and phosphorus: Emergency department testing yield. Acad Emerg Med 1997;4:559-563.

The objectives of this retrospective chart review were: 1) to determine how frequently ED ordering of calcium, magnesium, and phosphorus affected therapy in the ED or in the hospital; and 2) to suggest guidelines for selected ordering of these tests. During the nine-month study period, 1477 patients had at least one of the ions ordered in the ED. Of those, 260 patients had a total of 312 abnormal values. Rose and colleagues reviewed the charts of these patients to classify treatment into three groups: 1) no treatment for the abnormal lab value; 2) treatment administered in the ED; or 3) treatment administered in-hospital. Of the 1468 patients who had calcium determinations, only 10 (0.7%) had abnormal values. None received treatment in the ED. Of the 1444 patients who had a serum magnesium level ordered stat, 141 had abnormal values. Three of those patients received treatment in the ED. Of the 1448 patients who had a phosphorus level ordered in the ED, 161 had abnormal values. Two of those patients were treated in the ED.

Rose et al conclude that, had the testing been limited to certain subsets of patients (magnesium for alcoholics, calcium and phosphorus for patients with diabetes, and all three ions for patients with renal failure), or had the tests been ordered on a routine basis instead of stat, a significant cost savings would have been realized without compromising patient care.


This study helps confirm what most of us have suspected for quite some time—that mindless ordering of calcium, magnesium, and phosphorus in the ED is a waste of time and money and rarely results in any alteration of ED treatment. I cannot recall the last time I actually acted on an abnormal calcium, magnesium, or phosphorus value. By the time I see the magnesium value of an alcoholic patient, they are already receiving IV fluids with magnesium, thiamine, and other vitamins that give the fluids the characteristic "banana bag" appearance. (Isn’t it time we studied whether "vitamin resuscitation" beyond thiamine makes any sense in the ED?) In my experience, the calcium, magnesium, or phosphorus tests that come over our ED lab computer are ordered by students or residents from admitting services or well-intentioned nurses who try to expedite the patient’s ED work-up. As the "captain of the ship" in the ED, we attendings and faculty have a responsibility to make sure that diagnostic studies and treatments that are ordered are rational and in the patient’s best interests. We have a duty to educate nurses, our own students and residents, and those from other services about cost-effective laboratory testing.

Although the suggestions from Rose et al have not been prospectively studied, I think this study strongly supports their recommendations. If hypomagnesemia is clinically suspected, magnesium should be measured in alcoholic patients. Calcium and phosphorus determinations should be considered in diabetic patients who have acute complications of their disease. All three ions should be considered in patients who present with renal failure or in patients with complications of chronic renal insufficiency or failure. To be sure, there are other conditions where selective ordering of these ions is warranted. Patients with malignancies with change in mental status should have calcium measured. Patients with hyperparathyroidism frequently have hypercalcemia. Patients with acute tubular necrosis can have hypercalcemia. Drugs, pancreatitis, shock, and rhabdomyolysis are some of the conditions that can cause hypocalcemia. The point is that these ions do not need to be ordered as part of the "admission package," and if measuring these ions is indicated by clinical suspicion, they can frequently be ordered on a routine basis.