Evaluation of a laboratory critical limit (alert value) policy for hypercalcemia

To evaluate a laboratory critical limit policy for hypercalcemia requiring the laboratory to notify the physician for any serum calcium level higher than 2.99 mmol/L (12.0 mg/dL).

The protocol was assessed using the following criteria: recognition, treatment (fluids or drugs) or no treatment of hypercalcemia, and the effect of adopting lower (2.64 mmol/L) or higher (3.22 mmol/L) calcium critical limits.

Patients were divided into four groups: group 1, 2.64 to 2.74 mmol/L (n = 131); group 2, 2.77 to 2.87 mmol/L (n = 33); group 3, 2.89 to 2.99 mmol/L (n = 16); and group 4, higher than 2.99 mmol/L (n = 11). Hypercalcemia was recognized in 48%, 55%, 56%, and 100%; treated with fluids in 0%, 0%, 6%, and 9%; treated with drugs in 0%, 0%, 0%, and 73%; and not treated in 100%, 100%, 94%, and 18% of patients in groups 1 through 4, respectively. Lower calcium critical limits of 2.64, 2.77, and 2.89 mmol/L would lead to an increase of 1371%, 442%, and 142% in telephone calls. A higher calcium critical limit of 3.22 mmol/L would have resulted in not notifying the physician of six patients (60%) who were treated for hypercalcemia.

The present hypercalcemia policy is effective because patients with calcium levels below 2.99 mmol/L (< 1%) are rarely treated for hypercalcemia and because lowering the calcium critical limit alert value would not increase physician awareness of hypercalcemic patients. It would, however, result in a significant increase in telephone calls. A higher calcium critical limit (3.22 mmol/L) would potentially result in missing a significant number of hypercalcemic patients in need of therapy.