Point-of-care creatinine devices to assess kidney function before CT imaging with intravenous contrast

Point-of-care (POC) creatinine devices allow rapid measurement of creatinine levels and calculation of estimated glomerular filtration rate (eGFR). This can show whether the kidneys are working properly. The focus of this assessment is POC creatinine testing to assess kidney function before people have intravenous contrast for CT imaging. Intravenous iodine-based contrast agents used in CT scans can cause acute kidney injury (AKI), particularly in people who are at high risk and those with known kidney dysfunction. If a person has a low eGFR, intravenous hydration can be offered before the scan to reduce the risk of AKI. If a person does not have a recent eGFR measurement, their CT scan could be cancelled and rescheduled while a creatinine test is processed in the laboratory.

Using POC creatinine tests before outpatient contrast-enhanced CT scans in the radiology department could minimise the risk of kidney injury. It could also reduce the number of cancelled scans, which is important for patients.

AKI covers injury to the kidneys from a number of causes; it often happens as a complication of another serious illness. If AKI is not treated promptly, levels of salts and chemicals in the body can increase, which affects the fluid balance in the body and how well other organs work.

Post-contrast AKI (PC‑AKI) is a sudden deterioration in kidney function within 48 to 72 hours of administering intravenous iodine-based contrast agent. Incidence in patients having non-emergency CT scans with intravenous contrast agent is reported to be less than 1% (Ozkok et al. 2017). Risk factors for PC‑AKI include chronic kidney disease, critical illness, contrast-enhanced imaging done as an emergency, older age, diabetes, use of nephrotoxic drugs and reduced kidney function (for example, if a person is dehydrated or has congestive heart failure). Short- and long-term mortality rates are significantly higher in patients with PC‑AKI than in patients without PC‑AKI. A history of PC‑AKI may be also be associated with development of chronic kidney disease and progression to end-stage renal disease.

NICE's guideline on acute kidney injury: prevention, detection and management says that before using iodinated contrast agents for imaging, kidney function should be checked and the risk of AKI assessed. It recommends that eGFR should be measured within 3 months of using iodinated contrast agents.

The threshold for eGFR at which there is a risk of developing PC‑AKI varies across different guidelines, ranging between 30 ml/min/1.73 m² (The Royal Australian and New Zealand College of Radiologists iodinated contrast guidelines [2016], which have been endorsed by the Royal College of Radiologists) and 60 ml/min/1.73 m² (Renal Association guideline on the prevention of CI-AKI in adult patients [2013], in the Acute Kidney Injury guideline). Clinical experts suggested that people with an eGFR of less than 30 ml/min/1.73 m² are at highest risk of developing PC‑AKI.

Guidelines recommend that adults having iodinated contrast agents at increased risk of PC‑AKI should:

• be offered intravenous volume expansion

• consider temporarily stopping angiotensin-converting enzyme inhibitors and angiotensin receptor blockers

• have a nephrology team discuss their care if there are contraindications to intravenous fluids.

If PC‑AKI develops, NICE's guideline on acute kidney injury recommends:

• renal replacement therapy (dialysis) in some situations

• loop diuretics for treating fluid overload or oedema in people waiting to have dialysis, and in people who do not need dialysis.

Children were not included in the scope of this assessment because they often have alternative imaging, such as MRI scans, rather than CT scans. In addition, different eGFR equations are used for children and adults, so studies of POC creatinine devices in adult populations may not reflect the performance of these devices in children.