Which medications should be held 24+ hours before a contrast procedure?

• A. Metformin
• B. RAAS inhibitors
• C. Diuretics
• D. Acetaminophen

Answer: (B)

Hold medications that blunt the kidney’s ability to maintain filtration when contrast is used. Angiotensin system blockers—ACE inhibitors and ARBs—can reduce the pressure inside the glomerulus by preventing angiotensin II–mediated constriction of the efferent arteriole. In the setting of iodinated contrast, renal perfusion can dip, and losing this compensatory mechanism makes acute kidney injury more likely. So withholding these agents for at least 24 hours before the contrast study helps preserve GFR and lowers CIN risk. After the procedure, reassess and restart once renal function and volume status are stable.

Metformin is often held due to concerns about lactic acidosis if kidney function is impaired, diuretics can contribute to volume depletion, and acetaminophen is generally not a concern with contrast. The key idea here is that RAAS inhibitors can blunt renal autoregulation during contrast exposure, increasing AKI risk, so they are the meds commonly held 24+ hours before.