HHE Radiology and imaging supplement 2018 | Page 9

radiology and imaging
sponsored
Managing the risks of
contrast agents in imaging
Contrast carries a small, and controversial, risk of acute kidney injury, and the use
of a screening tool and point of care testing may provide the greatest opportunity
to streamline the imaging pathway and provide assurance of patient safety
Bev Snaith
PhD MSc DCR
Clinical Professor of
Radiography, Mid
Yorkshire Hospitals and
University of Bradford, UK
Martine Harris
MSc PGCert BSc (Hons)
Mid Yorkshire Hospitals
NHS Trust, UK
References
1 Royal Australian & New
Zealand College of Radiologists.
Iodinated contrast media
guideline. Sydney; 2016.
2 Davenport MS et al. Contrast
material-induced nephrotoxicity
and intravenous low-osmolality
iodinated contrast material: risk
stratification by using estimated
glomerular filtration rate.
Radiology 2013;268:719–28.
3 Kooiman J et al. Meta-analysis:
serum creatinine changes
following contrast enhanced
CT imaging. Eur J Radiol
2012;81:2554–61.
4 European Society of Urogenital
Radiology. ESUR guidelines on
contrast media, 2016. Version 9.
www.esur.org/esur-guidelines/
(accessed May 2018).
5 van der Molen AJ et al.
Post-contrast acute kidney
injury – Part 1: Definition,
clinical features, incidence, role
of contrast medium and risk
factors. Recommendations for
updated ESUR Contrast Medium
Safety Committee guidelines. Eur
Radiol 2018;doi: 10.1007/s00330-
017-5246-5.
6 Aycock RD et al. Acute
kidney injury after computed
tomography: a meta-analysis.
Ann Emerg Med 2017;71:44–53.
7 Harris MA et al. Strategies for
assessing renal function prior to
outpatient contrast-enhanced
CT: a UK survey. Br J Radiol
2016;89(1067):20160077.
8 Snaith B et al. Point-of-care
creatinine testing for kidney
function measurement prior to
contrast-enhanced diagnostic
imaging: evaluation of the
performance of three systems
for clinical utility. CCLM 2018;
doi:10.1515/cclm-2018-0128.
9 Korpi-Steiner NL et al.
Comparison of three whole
blood creatinine methods
for estimation of glomerular
filtration rate before radiographic
contrast administration. Clin
Chem 2009;132:920–6.
Imaging activity continues to rise across the
world, fuelled by growth in technology, screening
programmes and disease monitoring. The patient
safety implications around radiation are well
understood and there is increasing awareness of
the contraindications to other imaging procedures,
such as magnetic resonance imaging (MRI).
However, there are other safety-related concerns
associated, not with the imaging technology, but
with the drugs introduced to improve
visualisation of anatomy. The most high-profile
of these are the iodinated contrast agents used
in computed tomography (CT), interventional
radiology (IR) and cardiology procedures.
These contrast media are in fact iodine-based
‘dyes’ that are usually administered either
intra-arterially or intravenously to highlight
vascular and other anatomical structures on
imaging. There are two main concerns with these
agents:
• Allergic reaction to the iodine
• Acute kidney injury.
The risk of severe allergic reaction is rare,
only accounting for less than 1 in 100,000
patients, 1 with more common minor reactions
being nausea, vomiting and urticaria (rash).
The actual rate of occurrence of kidney injury
following contrast administration is difficult
to ascertain, but the risk is acknowledged to
be greatest in those patients with unstable and
reduced kidney function. 2 Although there remains
ongoing controversy as to its prevalence, authors
suggest it could represent between 1% and 20% of
patients, 3 greater in the acutely unwell patient
or when using higher doses of contrast media via
an intra-arterial route. 1,4,5 This iatrogenic problem
has a number of names, including contrast-
induced nephropathy (CIN), contrast-induced
acute kidney injury (CI-AKI) and, more recently,
post-contrast acute kidney injury (PC-AKI).
The latter is a relatively new term, 5 but, given
the mechanism of kidney injury is not well
understood, is accepted as a better representation
of the disease. 6
with reduced kidney function should be identified
to enable preventative measures to be initiated,
including hydration. Because of the volume of
patients involved and the limited knowledge of
comorbidities, identification of these patients
based on clinical history is unreliable. Screening
questionnaires are gaining in popularity and
allow patients to identify risk factors or pre-
existing conditions that might predispose them
to complications of the contrast. However, as
these forms are completed after arrival at the
imaging department, the ability to initiate
prophylactic hydration is limited, and this might
result in the scan being undertaken without
contrast or having the appointment rearranged.
As a result, many hospitals still require patients
to have a blood test for kidney function in
advance of the scan to prevent delays and
increase efficiency and safety.
Reducing and identifying the risks
So, if the contrast agents used can have
significant side effects, what are imaging
departments doing to reduce, or at least identify,
the risks? Kidney function testing
Most acutely unwell patients have already had
a panel of bloods results, including creatinine
and estimated glomerular filtration rate (eGFR),
measures of kidney function, whereas for
out-patients, this is commonly an additional test
and requires patients to have an additional
intervention, regardless of their co-morbidities
or risk status.
Whereas for most clinical specialities serum
creatinine and eGFR levels provide a longitudinal
comparison to identify trends in renal function,
imaging uses this as a single measure to
categorise the risk of PC-AKI. Although local and
national risk stratification varies, there is
agreement that the greatest risk of PC-AKI occurs
in those patients with an eGFR below 30ml/
min/1.73m 2 . Table 1 outlines the most common
thresholds and actions.
Although there is no consensus on the time
interval between kidney function testing and
contrast administration, this is often considered
to be acceptable within the preceding three
months, unless there is known or suspected
kidney dysfunction in which case a result
within the last week is advised. Unfortunately,
this information is not known until scan
day screening and therefore point of care
(PoC) testing is finding favour as a troubleshooting
tool.
Screening
International guidance advocates that patients PoC testing
Although a common site in other hospital and
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