Background: Serum magnesium is a commonly checked laboratory assay during hospital admissions. However, there is little evidence demonstrating benefit from ordering and repleting magnesium for most inpatients – including critically-ill patients.
Methods: Laboratory and magnesium repletion ordering data from 2015-2016 was obtained directly from laboratory and pharmacy databases for inpatient encounters with at least one plasma magnesium check.
Results: A total of 74,557 inpatient admissions were assessed. There was higher usage on housestaff general medicine teams (median 4, IQR 2-6) than for non-traditional teaching structure units (3, 1-5), which were similar between the two hospitals. Usage was higher in medical intensive care units (5, 2-10), but was consistent among cardiology, medicine, and oncology services. The median tests performed were similar when initial magnesium level was high (4, 2-9), low (4, 2-7), or normal (3, 1-6).
Conclusions: This usage analysis reveals that amongst two academic medical centers that there is frequent plasma magnesium assessment, and that there is little variation within non-ICU services. This uniform utilization and consistent ordering despite normal initial magnesium levels indicate that serum magnesium is frequently being ordered as a routine laboratory assay and not in response to clinical suspicion of low magnesium stores. There is little published evidence to justify this approach to magnesium assessment.