Serum magnesium levels in pediatric inpatients: a study in laboratory overuse

Hypomagnesemia, defined as a serum magnesium (Mg) level<1.5 mg/dL (0.62 mmol/L), is often asymptomatic. The goals of this study were to determine the incidence of clinically significant abnormal Mg levels in the inpatient setting and to identify diagnoses for which testing would be diagnostically helpful.

We obtained data from 2010 through 2011 on charges for serum Mg levels and Mg supplementation for all non-ICU inpatients from the 43 tertiary care children's hospitals in the Pediatric Health Information System database. A manual chart review was performed for all patients at our institution with charges for both Mg levels and Mg supplementation.

A median of 13.5% (interquartile range: 7.7-22.1) of non-ICU inpatients from Pediatric Health Information System centers had charges for Mg levels, at a total charge of $41 million in the 2010-2011 period. At our institution, 19.1% of non-ICU inpatients had charges for Mg levels, at a charge of $67.32/patient-day. Of the 4608 patients with Mg laboratory charges at our institution, 171 (3.7%) had an intervention, defined as addition or modification of an Mg supplement dose in response to a serum Mg level. The 4 most common groups of diagnoses (oncologic, abdominal surgery requiring total parenteral nutrition, solid organ transplant, and short bowel syndrome) accounted for 143 (83.6%) of these interventions.

Serum Mg levels were frequently ordered in non-ICU inpatients, but levels were seldom abnormal and rarely resulted in changes in clinical management. These findings raise concerns about resource overutilization and provide a target for more judicious laboratory ordering practices.