Preparing for a CT Scan With Contrast: What You Need to Know

If your doctor ordered a CT scan "with contrast," you might have questions. What is contrast? Why do you need it? Is it safe? Here's everything you need to know.

What Is CT Contrast?

CT contrast (sometimes called "contrast dye") is a special liquid containing iodine that makes certain structures show up more clearly on the scan. It can be given intravenously (IV), orally, or both.

Why Is Contrast Needed?

Without contrast, many structures look similar on CT. Contrast helps distinguish tumors from normal tissue, visualize blood vessels and detect clots, show areas of infection or inflammation, and evaluate organ function.

Not every CT needs contrast — many bone, lung, and kidney stone studies are done without it.

How to Prepare

For IV Contrast: - **Blood test:** You may need a recent creatinine/GFR test to check kidney function - **Hydration:** Drink plenty of water before and after - **Fasting:** Some protocols ask you not to eat for 2-4 hours before - **Metformin users:** Ask your doctor about holding the dose for 48 hours after

For Oral Contrast: - You'll be given a flavored drink to consume over 1-2 hours before the scan - Follow timing instructions carefully

During the Exam

When IV contrast is injected, most people experience: - A warm, flushed feeling spreading through the body — completely normal - A metallic taste in the mouth — brief and harmless - A sensation of warmth in the pelvis — feels unusual but is not dangerous

These sensations last 30-60 seconds.

Contrast Allergies

True allergic reactions are uncommon (about 1-3% of patients). Most are mild: hives, itching, or nausea. Severe reactions (difficulty breathing, anaphylaxis) are rare — less than 0.04%.

If you've had a prior reaction: Tell your doctor and our staff. You may be premedicated with steroids and antihistamines.

Shellfish allergy: Despite popular belief, this does NOT increase your risk of contrast reaction.

After the Exam

• **Drink extra water** for 24 hours to help flush contrast
• **Resume normal activities immediately**
• **Watch for delayed reactions** (rare): hives or swelling within a few hours

Questions?

Call us at (727) 398-5999. Our team can answer your questions about contrast, preparation, and what to expect.