Evaluation of total serum calcium critical values.

Context: As a patient safety measure, laboratories are required by regulatory agencies to have a critical values policy. Total serum calcium commonly is included in critical results lists; however, a wide range of values are used and there is scant outcome data justifying inclusion of this analyte in these lists.

Objective: To evaluate the appropriateness of the critical values for total serum calcium used in our institution.

Design: We studied all critical total serum calcium results found during a 3-month period. The patients' medical records were evaluated for the presence of documented critical results call for calcium, clinician response, and patient outcome. The patients' outcomes were measured by time of clinical response, length of stay in the hospital, and mortality.

Results: There were 722 (1.4%) critical results found in a total of 50 402 total serum calcium results. Using our criteria of 7 mg/dL or less as the low and 12 mg/dL or more as the high critical value, we found 171 patients with 608 critically low results and 47 patients with 114 critically high results. Eighty percent of patients with critically low results and 75% of patients with critically high results had length of stays greater than our average (5.58 days). Clinicians responded to 49% of the critical results calls within 4 hours. There was an overall mortality rate of greater than 25%, with more than half the mortality occurring in patients who had results within 0.5 mg/dL of the cutoff values used.

Conclusion: Although broadening critical values limits would reduce required calls, this does not appear warranted. The disease severity of the patients as measured by length of stay and mortality, as well as the rapidity with which patients were treated, indicate that the current limits are appropriate and should not be widened.