Effect of low-osmolality intravenous contrast on serum osmolal gap in adults

Background: Contrast media used today is considered "low-osmolality. " No study has evaluated the effect of intravenous contrast media on the measurement of the osmolal gap in adult patients. Objective: To determine if "low-osmolality" intravenous contrast media administered to adult patients undergoing computed tomography (CT) of the abdomen and pelvis affects the osmolal gap. Methods: We performed a prospective pilot study in the Emergency Department of a university-affiliated tertiary care center. Patients were enrolled if they were age ≥18 years and <60 years and the treatment team had ordered an abdomen and pelvis CT with intravenous (i.v.) contrast procedure and a serum basic metabolic panel (BMP) that included serum glucose, blood urea nitrogen, and sodium. Once enrolled, a serum osmolality and serum ethanol level was ordered and obtained on the same blood draw as the BMP before the CT. Patients were excluded if they had detectable ethanol on laboratory screen, if they were suspected to have ingested methanol, ethylene glycol, isopropanol, mannitol, or underwent CT with i.v. contrast within the prior 24 h. Paired samples were compared using the Wilcoxon signed-rank test. Results: Of the 100 patients screened, 18 patients were lost due to withdrawal of consent or missing data. The median of the osmolal gap pre-CT was 8.18 with an interquartile range of 4.76-11.15. The median of the osmolal gap post-CT was 11.23 with an interquartile range of 7.29-14.83. The difference in the osmolal gap was a median of 2.34 (p = 0.0003) with an interquartile range of 1.32-5.97. Conclusion: Although the effect in our study was small, clinicians should be aware of the ability of contrast media to increase the osmolal gap.