Diabetes affects nearly every organ system in the body, so CT scans can be ordered for a wide range of complications, from blocked arteries in the legs to serious kidney infections to unexplained foot pain that could signal a bone infection. The scan itself isn’t specific to diabetes. Rather, the conditions diabetes causes or worsens are what make CT imaging so common for people living with the disease. Here’s a breakdown of the most likely reasons, plus what you need to know about scan safety when you have diabetes.
Checking Blood Flow in the Legs
One of the most common reasons is peripheral arterial disease, a condition where arteries in the legs become narrowed or blocked. Diabetes accelerates the buildup of fatty deposits and calcium in artery walls, so circulatory problems in the lower limbs are far more frequent and tend to be more severe. A CT angiography scan (a CT with contrast dye focused on blood vessels) gives doctors a detailed map of where blockages are, how extensive they are, and how severely blood flow is reduced.
CT angiography is highly accurate for this job, with sensitivity of 95 to 97% and specificity of 91 to 98% for detecting significant narrowing or complete blockages, particularly in the larger arteries of the thigh and upper leg. It’s less precise for the smaller vessels below the knee and for arteries that are heavily calcified, both of which are common in diabetes. Newer scanning techniques can digitally subtract the calcium from the image, making it easier to see the actual opening inside the artery. The results help determine whether you need medication alone, a procedure to open the artery, or surgery to bypass it.
Evaluating Diabetic Foot Infections
Foot ulcers are a well-known complication of diabetes, and one of the biggest concerns is whether an infection has spread from the skin down into the bone, a condition called osteomyelitis. CT imaging, sometimes combined with a nuclear medicine scan, can help determine whether bone is involved. The diagnostic accuracy of this combined approach is comparable to MRI, with sensitivity around 89% and specificity around 35%. MRI is generally preferred when available, but CT-based imaging is a useful alternative when MRI isn’t an option, for example if you have a pacemaker or other metal implant.
Knowing whether infection has reached the bone changes the treatment plan significantly. A soft tissue infection may respond to a few weeks of antibiotics, while osteomyelitis often requires months of treatment or, in some cases, surgery to remove the infected bone.
Diagnosing Serious Kidney Infections
People with diabetes are at higher risk for a rare but life-threatening kidney infection called emphysematous pyelonephritis. In this condition, gas-producing bacteria infect the kidney, and the trapped gas pockets are clearly visible on a CT scan. This is one situation where CT is the go-to imaging tool because it can show exactly where the gas is, whether it has spread beyond the kidney, and whether there are kidney stones contributing to the problem. Rapid diagnosis with CT is critical because this infection can become fatal without prompt treatment.
Assessing Heart and Stroke Risk
Diabetes significantly raises the risk of heart attack and stroke. CT scans can be used to evaluate calcium buildup in the coronary arteries (a marker for heart disease risk) and to check for blockages in the arteries supplying the brain. If you arrive at an emergency room with stroke symptoms, a CT of the head is typically the first imaging test ordered, regardless of your diabetes status. But having diabetes makes these events more likely in the first place, which is why diabetic patients end up getting these scans more often.
CT can also pick up signs of more severe atherosclerosis in the arteries around the pancreas and signs of liver disease, both of which are more common in people with type 2 diabetes. Sometimes these findings are discovered incidentally on a scan ordered for something else entirely.
Other Common Reasons
Beyond the complications above, a CT scan might be ordered for a diabetic patient for many of the same reasons it’s ordered for anyone: abdominal pain, suspected appendicitis, cancer screening, or trauma after an injury. The difference is that diabetes makes certain emergencies more likely and can mask symptoms. Reduced sensation from nerve damage, for example, can mean you don’t feel the severity of an abdominal infection until it’s advanced. Doctors may have a lower threshold for ordering imaging in diabetic patients because of this.
Why Contrast Dye Needs Extra Caution
Many CT scans require an injection of iodine-based contrast dye to make blood vessels and organs show up more clearly. For most people, this is straightforward. For people with diabetes, there’s an added concern: contrast dye can temporarily stress the kidneys, and diabetes often comes with some degree of existing kidney impairment.
The risk of contrast-related kidney injury increases with age and the severity of existing kidney disease. In one study of patients undergoing heart procedures, the rate of kidney injury after contrast exposure was 8% for diabetic patients under 50, 12% for those aged 50 to 69, and 18% for those 70 and older. Current evidence suggests there is no meaningful risk of kidney injury when your kidney filtration rate (eGFR) is 45 or above. Below that threshold, the risk becomes more significant and extra precautions are taken.
If your kidney function is reduced, you’ll likely receive IV fluids (saline) before and after the scan to help flush the contrast through your kidneys more quickly. The radiologist may also use the smallest effective amount of contrast dye.
Metformin and CT Scans
If you take metformin, one of the most widely prescribed diabetes medications, your care team will have specific instructions around the scan. Metformin is processed by the kidneys, and if contrast dye temporarily reduces kidney function, metformin can build up to unsafe levels in the blood and cause a dangerous condition called lactic acidosis.
The general approach is to stop metformin at the time of the scan. If your kidney function is already reduced (eGFR below 60), you’ll typically be told not to restart it for at least 48 hours, and only after a blood test confirms your kidneys have recovered. If your kidney function is normal and the scan uses a smaller volume of contrast (under 100 mL, as in a brain CT), pausing metformin may not even be necessary. For larger contrast volumes, like those used in abdominal or vascular scans, the 48-hour pause generally applies even with normal kidney function.
This doesn’t mean the scan is dangerous. It means your medical team needs to plan around your medication timing. You should bring a list of your current medications to any imaging appointment so the technologist and radiologist can adjust the protocol accordingly.
Managing Blood Sugar Around the Scan
Some CT scans require fasting for several hours beforehand, which can be tricky when you’re managing blood sugar with insulin or oral medications. Skipping a meal without adjusting your medication can cause blood sugar to drop too low, while the stress of a medical procedure can push it higher. If you’re told to fast before a scan, ask your doctor whether you need to adjust your insulin dose or the timing of your other diabetes medications. Bringing a quick-acting sugar source like glucose tablets to the appointment is a practical safeguard in case your blood sugar dips while you’re waiting.