What is the standard adult dose of intravenous iodinated contrast for CT and gadolinium‑based contrast for MRI, and how should the dose be modified in patients with eGFR < 30 mL/min/1.73 m² or iodine/gadolinium allergy?

Standard Intravenous Contrast Dosing

CT Iodinated Contrast: Standard Adult Dose

For CT angiography, administer 1.2 mL/kg of 350 mg iodine/mL at 4 mL/s injection rate, which achieves mean pulmonary artery opacification of 250 HU on 64-detector CT. 1

Weight-Based Dosing Protocol

• Standard protocol: 1.2 mL/kg body weight using 350 mg iodine/mL concentration 1
• Flow rate: 4-5 mL/s for standard patients; increase to 5-6 mL/s for BMI >30 kg/m² 1
• Minimum volume: At least 90 mL for patients with elevated BMI 1
• Venous access: 20-gauge fenestrated catheter in antecubital vein (allows 5.0-7.5 mL/s flow) or 18-gauge standard catheter 1

Concentration Selection

• Prefer 350 mg iodine/mL over 300 mg/mL: Lower total volume achieves equivalent enhancement without compromising diagnostic quality 1
• Avoid 240 mg iodine/mL: Inferior contrast enhancement index except in patients <73 kg 2

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MRI Gadolinium Contrast: Standard Adult Dose

Administer 0.1 mmol/kg body weight of gadolinium-based contrast media (GBCM) as the standard dose for MRI. 1

Agent Selection by Safety Profile

• Group II agents (macrocyclic): Gadobutrol, gadoterate, gadoteridol—extremely low NSF risk even in severe renal impairment 1
• Group III agents: Gadoxetate disodium—no unconfounded NSF cases reported, primarily for liver imaging 1
• Avoid Group I agents (linear): Associated with 190-fold higher NSF rate versus Group II agents 1

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Dose Modification in Renal Impairment (eGFR <30 mL/min/1.73 m²)

Iodinated Contrast in Severe CKD

Iodinated contrast is NOT contraindicated at eGFR <30 mL/min/1.73 m² but requires mandatory preventive measures. 3

Required Preventive Protocol

• Hydration: Isotonic saline (0.9% NaCl) before, during, and after procedure (Class I, Level A recommendation) 1, 3
• Minimize volume: Use lowest diagnostic dose while maintaining image quality 1
• Avoid high-osmolar agents: Use only low- or iso-osmolar contrast 1
• Withdraw nephrotoxins: Stop NSAIDs, aminoglycosides, metformin 48 hours before procedure 1
• Post-procedure monitoring: Measure eGFR at 48-96 hours 1

eGFR-Specific Thresholds

• eGFR ≥45 mL/min/1.73 m²: No additional precautions needed; contrast is not an independent nephrotoxic risk 3
• eGFR 30-44 mL/min/1.73 m²: Contrast permitted with mandatory hydration and reduced volume 1, 3
• eGFR <30 mL/min/1.73 m²: Heightened caution but not contraindicated; apply all preventive measures 1, 3
• eGFR <15 mL/min/1.73 m²: Contrast may be given when diagnostic benefit outweighs risk 3

Gadolinium in Severe CKD

For eGFR <30 mL/min/1.73 m², use only Group II macrocyclic chelate preparations at standard dose (0.1 mmol/kg). 1

• eGFR 15-29 mL/min/1.73 m²: Preferentially use macrocyclic agents; NSF risk extremely low with Group II agents 1
• eGFR <15 mL/min/1.73 m²: Avoid gadolinium unless no alternative test exists; if essential, use only Group II agents 1
• Dialysis patients: No prophylactic dialysis needed after Group II gadolinium at standard dose 4

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Contrast Allergy Management

Iodinated Contrast Allergy

Shellfish or povidone-iodine allergy is NOT a contraindication to iodinated contrast—these are unrelated to true contrast hypersensitivity. 1

Key Allergy Principles

• Iodine is not an allergen: Reactions are non-IgE-mediated mast cell activation, not iodine hypersensitivity 1
• Shellfish allergy: Caused by tropomyosin protein, not iodine; no cross-reactivity with contrast 1
• Povidone-iodine reactions: Do not predict contrast reactions 1
• History of severe contrast reaction: Absolute contraindication; consider alternative imaging or gadolinium for vascular procedures 5

Gadolinium as Alternative

• For true iodinated contrast allergy: Gadolinium has different chemical structure with no cross-reactivity 5
• Dosing for angiography: Higher than standard MRI doses may be required for adequate vascular opacification 5

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Critical Pitfalls to Avoid

• Do not rely on serum creatinine alone: Always calculate eGFR using MDRD or CKD-EPI equation 3
• Do not withhold contrast at eGFR >30 mL/min/1.73 m²: Risk-benefit strongly favors diagnostic imaging over theoretical nephrotoxicity 3
• Do not assume all contrast is equally nephrotoxic: Large cohort studies dispute causal relationship between IV contrast and AKI at eGFR >45 mL/min/1.73 m² 3
• Do not use body weight alone in obese patients: Body fat percentage affects enhancement; heavier patients may receive excessive contrast if dosed by weight alone 6, 2
• Do not schedule prophylactic dialysis after gadolinium: No evidence supports this practice with Group II agents, even in dialysis-dependent patients 4