Hypocalcemia: An Underrecognized Problem in Older Adults
This past week, I have had several patients with abnormal serum calcium levels, both high and low, and thought it would be a good idea to remind others about the problem of hypocalcemia. While hypercalcemia is not an infrequent finding in the older person, few physicians expect to see low calcium values. If they are noted on the laboratory results, they usually assume that they are due to low protein binding; total calcium levels are usually what have been measured. Patients with true hypocalcemia are not uncommon if one looks hard enough or sees patients in the setting of acute illness. In fact, one study reported that 70% of patients in a medical Intensive Care Unit had a low serum calcium level at some time during their admission.1 Of note, the exact cause of the hypocalcemia could be identified in only 45% of these cases. While it is not cost-effective to measure an ionized calcium on all patients, one must clearly recognize that this is the only way to truly measure the functional level of calcium in persons with low protein binding and may be a necessary test under certain circumstances.
There are many causes of hypocalcemia, including hypovitaminosis D, acute pancreatitis, rhabdomyolysis, massive tumor lysis, phosphate infusion, toxic shock syndrome, acute severe sepsis, alkalosis, “hungry bone syndrome” (post-parathyroidectomy), anticalcemic/osteoporosis agents such as bisphosphonates, antineoplastic agents (eg, doxorubicin, cisplatinum), ketoconazole, pentamidine, hypomagnesemia, blood transfusions, hyperphosphatemia, hypoparathyroidism, and even cancer, especially prostate and breast. While most only consider a malignancy when they have a patient with hypercalcemia, both prostate and breast cancer in the setting of osteoblastic metastases have been associated with this finding.
So, the next time you see a low serum calcium level, please do not assume it is an error or due to low protein binding. Determine whether there is an albumin to evaluate; remember that for every 1.0 gram the serum albumin level is below normal, you can add 0.8 grams of calcium to the measured total serum calcium level. See if this improves the serum calcium to normal. If there is any doubt, you will need to obtain an ionized calcium level. Clinically, you can look for a prolonged QT interval on the electrocardiogram and see if the patient exhibits a Trousseau or Chvostek sign; these are evidence of low levels affecting physiological function and must be taken seriously. Very low levels may be associated with ventricular arrhythmias, elevated blood pressure, tetany, laryngospasm, and even seizures. Treat hypocalcemia with calcium, and correct the underlying pathology if identified. Monitor serum levels, and ask for assistance if you are not sure how best to proceed.
I hope you will be on the lookout for this potentially life-threatening problem.
Dr. Gambert is Professor of Medicine and Associate Chair for Clinical Program Development, Co-Director, Division of Gerontology and Geriatric Medicine, Department of Medicine, University of Maryland School of Medicine, Director, Geriatric Medicine, University of Maryland Medical Center and R Adams Cowley Shock Trauma Center, and Professor of Medicine, Division of Gerontology and Geriatric Medicine, Johns Hopkins University School of Medicine, Baltimore, MD.
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1. Desai TK, Carlson RW, Geheb MA. Prevalence and clinical implications of hypocalcemia in acutely ill patients in a medical intensive care setting. Am J Med 1988;84:209-214.