Contrast-associated acute kidney injury after scans

Iodinated contrast makes blood vessels and organs show up clearly on X-ray based imaging. It is filtered out through the kidneys and passes out in the urine; the NHS CT page notes this. In concentrated form it can transiently reduce blood flow within the kidney and irritate the tubular cells, which in vulnerable people shows up as a rise in creatinine, usually peaking within a few days and settling over one to several weeks.

The condition is described as contrast-associated when the rise follows contrast but other causes, such as low blood pressure, infection or other drugs, may also have played a part. Clinicians have become more cautious about attributing every post-scan dip to the dye, because acutely unwell patients who need contrast are already at risk of kidney injury from their illness.

The NHS asks people to tell staff before a CT scan if they have kidney or thyroid problems. Risk rises with pre-existing chronic kidney disease, particularly at the lower eGFR stages, and with diabetes, heart failure, dehydration, older age, recent acute kidney injury and the use of certain medicines. Large volumes of contrast, repeat doses within a short interval, and intra-arterial injection at angiography raise the exposure.

• Existing chronic kidney disease, particularly stage 3b to 5.

• Dehydration from vomiting, diarrhoea or poor fluid intake.

• Heart failure or low blood pressure at the time of the scan.

• Recent acute kidney injury or sepsis.

• Regular use of NSAIDs, diuretics or ACE inhibitors, which are sometimes paused around contrast on specialist advice.

Teams usually check recent kidney blood tests for people with risk factors, choose whether an alternative scan such as ultrasound or MRI without gadolinium would answer the question, and use the lowest dose of contrast that gives a diagnostic image. Encouraging oral fluids, or giving intravenous fluids to people who are at high risk and unable to drink, is the most established preventive measure.

Some medicines may be held for a short time around the scan on the instruction of the team; do not stop prescribed medicines on your own. After the scan, a repeat blood test two to three days later is commonly arranged for higher-risk patients so that any rise is spotted and managed early.

Most people feel nothing. The condition is detected by a rise in creatinine, a fall in eGFR or reduced urine output. When symptoms do occur they mirror those of acute kidney injury in general: passing less urine, nausea, tiredness, swelling and shortness of breath. Diagnosis is confirmed with blood tests and, if the cause is unclear, a urine test and an ultrasound to exclude a blockage.

There is no specific antidote. Care is supportive: stopping or adjusting medicines that stress the kidneys, correcting dehydration, treating any infection, monitoring potassium and fluid balance and repeating blood tests until function recovers. Dialysis is rarely needed and is reserved for severe injury, dangerous potassium levels or fluid overload.

Most people recover within days to weeks. Because an episode of acute kidney injury increases the chance of later chronic kidney disease, people who had one are often advised to have kidney function rechecked after about three months and to be cautious with anti-inflammatory painkillers.

Contrast can also provoke an allergic-type reaction, which is a different mechanism from kidney injury. The NHS notes that some people have an allergic reaction to the contrast medium, with weakness, sweating or breathing difficulty, which is why patients wait in the department for up to 30 minutes afterwards. A previous reaction should always be mentioned beforehand. Hot flushes and a metal taste during injection are common, brief and harmless.