Intravenous Contrast Agents and Associated Changes in Serum Osmolality

Abstract

Anecdotal data suggest that intravenous contrast agents given to enhance the sensitivity of computed tomography (CT) can produce increases in serum osmolality, producing an osmolal gap. An unexplained osmolal gap often prompts extensive evaluation for the presence of unidentified toxins, particularly the toxic alcohols (methanol, ethanol, isopropyl alcohol, and ethylene glycol). The ability of intravenous contrast media to raise serum osmolality with a resulting osmolal gap has not been systematically investigated. We evaluated changes in serum osmolality and osmolal gap in a cohort of patients presenting to a pediatric emergency department with abdominal pain who necessitated a contrast-enhanced CT scan as part of their diagnostic evaluation. Inclusion criteria were age of 10 to 18 years and the ability to obtain blood samples 30 minutes after contrast administration. Before and 30 minutes after contrast administration, serum osmolality and Na, glucose, and serum urea nitrogen levels were obtained. Osmolal gap was calculated using the formula 2(Na) + serum urea nitrogen/2.8 + glucose/18. The contrast agent Optiray 320 (Tyco healthcare, Mallinkrodt, Hazelwood, Mo) (ioversol, 68%) was administered at a dose of 2 mL/kg (1.36 g/kg). The main outcomes of interest were precontrast versus postcontrast osmolality and osmolar gap. Fourteen subjects were enrolled. The mean precontrast and postcontrast serum osmolalities were 292.75 and 292.875 mOsm/L (P = 0.93), respectively. The corresponding mean values for the precontrast and postcontrast osmolal gaps were 9.17 and 12.15 mOsm/L, respectively (P = 0.133). The mean difference between the precontrast and the postcontrast osmolal gaps was 0.125 mOsm/L. There was no statistically significant correlation between the dose of the contrast agent administered and the postcontrast osmolality or osmolal gap. These data suggest that intravenous contrast agents, when administered at conventional doses, do not significantly increase serum osmolality or produce an osmolal gap. Patients who are found to have an osmolal gap after the performance of a contrast-enhanced CT scan should undergo thorough evaluation to identify its etiology rather than attributing the gap to contrast administration.