Acute kidney injury: prevention, detection and management

Why the committee made the recommendations

The evidence for the accuracy of risk assessment tools or questionnaires to predict an acute kidney injury after administration of iodine-based contrast media was lacking in both quantity and quality. The majority of the risk prediction tools were included in a small number of studies, with low numbers of participants and a younger population than would usually be seen in practice, so limiting the certainty of their accuracy. Therefore, the committee made recommendations based on their knowledge and expertise. They also made a recommendation for research on what validated risk assessment tools should be used to predict contrast-associated acute kidney injury following intravenous iodine-based contrast media.

The evidence for the prognostic accuracy of estimated glomerular filtration rate (eGFR) for iodine-based contrast media-associated acute kidney injury showed that a lower eGFR is associated with an increased risk of acute kidney injury. No evidence was found comparing an eGFR threshold of 30 ml/min/1.73 m² with the currently recommended threshold of 40 ml/min/1.73 m². However, the committee agreed that an increased risk is associated with an eGFR less than 30 ml/min/1.73 m², and this is currently used to indicate poor kidney function.

In current practice, a person is required to have an eGFR test in the 3 months before undergoing contrast media CT scanning. This often results in delayed scans and increases the burden on patients and clinicians to conduct blood tests that may not be needed. In non-emergency settings, the committee agreed that if an eGFR test from within the past 6 months is available, this should be used to support decisions on contrast media scans. Using an eGFR from the previous 6 months as a reference would be an acceptable reflection of a person's eGFR at the time of iodine-based contrast media use if the person had been clinically stable since the last test. If a recent eGFR is not available, screening questions could be used to assess risk. By including initial questions on pre-existing kidney disease, a large proportion of people would not need blood tests. This is a simple assessment, and if the responses indicate a history of kidney disease, this should prompt clinicians to consider requesting an eGFR test.

The committee noted that people known to have kidney disease would usually have an eGFR result from the past 6 months, because people with a long-term chronic illness are more likely to have regular blood tests to monitor their condition. If a person is acutely unwell at the time of contrast use, an up-to-date blood test would be expected as part of normal practice.

In life-threatening or emergency situations, risk prediction tools should not be applied, and iodine-based contrast media should be administered without delay, if the risk of delaying is likely to be clinically significant.

How the recommendations might affect practice

The recommendations in this update are likely to reduce the volume of eGFR testing, with a set of screening questions removing the need for an eGFR test in people who have a low risk of kidney disease. The recommendation to use an eGFR value from the past 6 months will further reduce the need for testing, resulting in fewer scans being cancelled at short notice.

The committee noted that in practice, clinicians currently use a threshold of 30 ml/min/1.73 m², despite NICE having recommended 40 ml/min/1.73 m². Therefore, the new threshold of 30 ml/min/1.73 m² is not expected to cause a significant change in practice and may further reduce the need for scan cancellations where clinicians had previously followed NICE guidance. Because only people with the greatest risk would need an eGFR test, this new threshold would be cost saving to the NHS because of the reduction in eGFR testing.

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Why the committee made the recommendations

For adults undergoing procedures with intravenous iodine-based contrast media, the evidence showed that oral fluids were as good as intravenous fluids at preventing contrast-induced acute kidney injury. The evidence did not show that any particular type of oral or intravenous fluids is most effective.

The committee agreed that intravenous fluids are not necessary for outpatients who are usually at a lower risk of contrast-induced acute kidney injury. It also agreed that only inpatients at particularly high risk needed intravenous fluids. Most of the risk factors were agreed when the 2013 version of the guideline was developed – apart from the level of eGFR, which was based on the committee's clinical knowledge and experience in the 2019 update of this section. The committee also agreed that, based on their experience and expertise, the risk for intra-arterial administration depends on the site of the injection, and is particularly high with first-pass renal exposure because the contrast medium passes into the kidneys relatively undiluted.

For inpatients at particularly high risk of contrast-induced acute kidney injury, economic modelling showed that intravenous volume expansion with a regimen containing intravenous sodium chloride 0.9% and/or intravenous sodium bicarbonate provides best value.

Based on the evidence, the committee decided that intravenous volume expansion should be used only for inpatients at particularly high risk and that oral hydration should be encouraged in all other adults at increased risk of contrast-induced acute kidney injury.

The committee agreed that more research on estimating the risk of contrast-induced acute kidney injury would help to inform future guidance, so made a recommendation for research on the use of eGFR thresholds to stratify risk.

Although the committee agreed that oral hydration regimens were non-inferior to intravenous hydration regimens at preventing contrast-induced acute kidney injury, there was not enough comparative data to enable them to be clear about which oral fluid (if any) was most effective. There was some limited evidence that N-acetylcysteine was not beneficial. However, the committee agreed that, in the absence of evidence of harm, this was not sufficient to make a recommendation to restrict its use. Therefore, it made a recommendation for research on different oral fluids and different oral fluid regimens, with and without N-acetylcysteine.

The committee did not consider it necessary for all patients being offered iodine-based contrast media to be routinely discussed with a nephrology team, but concluded that this was important for adults on renal replacement therapy, including people with a kidney transplant. The radiology team responsible for administering the contrast medium or the healthcare professional offering the procedure, such as a cardiologist, would usually do this. For people with other contraindications to intravenous fluids, the committee agreed that the decision to give iodine-based contrast media was better made by individual healthcare professionals.

How the recommendations might affect practice

The recommendations may result in lower resource use for outpatient procedures because people will not need to be admitted to hospital to be given intravenous fluids for volume expansion before they are given a contrast medium.

The recommendation on intravenous volume expansion reflects current practice so there should be no change in practice for inpatients who are at particularly high risk of contrast-induced acute kidney injury. There may be reduced resource use for lower risk inpatients who will not need intravenous fluids.

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