Total Calcium and Ionized Calcium (pH = 7.4) Tests Are Equal When Screening Patients for Hypercalcemia at Admission in the Emergency Department: A Retrospective Descriptive Study

Background: Ionized calcium (pH = 7.4) (Cal) is a laborious test compared to tests for total calcium (CaT). However, Cal is the biologically active part of calcium in the blood and is therefore often considered the most relevant measure of calcium status. In this study, Cal and CaT tests were compared by identifying clinically relevant hypercalcemia (HC) in unselected patients acutely admitted to an emergency department (FD). Methods: Cal and CaT were measured in all medical patients admitted to the ED at a single Danish Hospital (N = 13,400) between January 2018 and May 2019. The majority (97%) of the patients were admitted 1 - 3 times summing up to a total of 17,838 admissions. As limits for clinically relevant HC, 1.45 mmol/L for Cal . and 2.77 mmol/L for CaT were used. Mismatches were defined as one test being equal to or above the limit while the other test was within or below its reference interval. In cases of mismatch, the medical record was reviewed. Results: Seventeen mismatches with Cal >= 1.45 mmol/L were observed in 16 patients, of whom eight were known with diseases with risk of HC. Five patients had HC with no clinical relevance, one had HC of unknown relevance, and only two patients were discovered as having a prior unknown calcium metabolic disease. Three mismatches were observed in admissions with CaT >= 2.77 mmol/L. Mismatches did in none of these cases have any clinical consequences. Conclusion: By using CaT as a screening method for HC instead of Cal, only two patients with prior unrecognized HC would have been missed and it did not result in a large number of patients with false HC. We therefore find that CaT is an acceptable test when screening for HC in the ED.