The dose of iodinated contrast required for a CT scan is below the toxicological threshold of concern for nephrotoxicity: a toxicological perspective

Observational and retrospective studies have demonstrated an apparent association between administration of intravenous contrast and subsequent development of acute kidney injury (AKI). This condition is termed contrast associated acute kidney injury (CA-AKI). The CA-AKI literature has focused on contrast administration in the setting of percutaneous coronary intervention (PCI) rather than computed tomography (CT). The dose of contrast for PCI is significantly higher than that for CT, and extrapolating the risks of a medicine at high dose to low dose may imply a risk that does not exist. Multiple recent studies (notably Hinson 2017, Aycock 2018, and Ehmann 2023) assessing the relationship between AKI and low-dose contrast administration, i.e., that required for CT, found no association with renal injury. The degree of toxicity of any substance exists on a continuum, and there is a dose below which there is no toxicity, called the toxicological threshold of concern (TTC). There is sufficient evidence to imply that the contrast doses for a single CT scan is below the TTC. Since the maximum typical contrast dose for a single CT is 120 mL of a 350 mg/mL solution, this dose appears to be below the TTC. The dose for CT scan is a fraction of that for PCI, and while there may be a small risk of CA-AKI with doses required for PCI the literature indicates there is minimal risk of CA-AKI with the contrast dose required for a CT, indicating a toxicological threshold of concern of 120 mL. Simply put, the 200-900 mL of contrast required for PCI might cause CA-AKI, whereas no evidence suggests the 60-120 mL of contrast required for a single CT scan would.