CT with IV contrast in low renal function
In CT with IV contrast, decreased renal function and several other conditions increase the risk of contrast-induced nephropathy, which is a potentially lethal renal injury to the kidney following intravenous radiocontrast.
When it matters
According to European guidelines, the main risk factors of contrast-induced nephropathy:
- Estimated glomerular filtration rate (eGFR) of less than 30 ml/min/1.73 m2 before intra-venous or intra-arterial radiocontrast administration with second-pass renal exposure (passing lungs or other tissues before the kidneys).
- eGFR can be calculated from creatinine level, age, sex and race (link to calculator), but is even more accurately given by the addition of height, weight, stability of creatinine as well as any amputations (link to calculator.
- eGFR is preferably calculated by cystatin C rather than creatinine in patients with abnormal muscle mass or cirrhosis.
- eGFR of less than 45 ml/min/1.73 m2 before intra-arterial administration with first-pass renal exposure or in ICU patients
- Known or suspected acute renal failure
- Large doses of radiocontrast given IA with first-pass renal exposure
- Multiple radiocontrast injections within 48-72 h
Other risk factors
Look in the medical records (and/or ask the patient) for other risk factors of contrast-induced nephropathy.
The Roxana Mehran score predictor applies the following ten variables:
- Age (4 points if older than 75 years old)
- Anemia (3 points)
- Use of an intra-aortic balloon pump (5 points)
- Decreased real function. In terms of estimated glomerular filtration rate in ml/min:
- eGFR 60 to 40 (2 points)
- eGFR 40 to 20 (4 points)
- eGFR less than 20 (6 points)
- Hypotension (5 points, if systolic BP less than 80 mmHg for at least one hour requiring inotropic support)
- Contrast media volume (1 point per 100 ml)
- Congestive heart failure (5 points)
- Diabetes (3 points).
A risk score of less than 6 carries a risk of 7.5% to score more than 16 carries up to 57% risk.
In addition to those in the Roxana Mehran score, the following are also risk factors of contrast-induced nephropathy:
- NSAIDs or (other) nephrotoxic drugs
- Persons in dialysis with residual renal function of at least 400 ml urine / 24h
- Individuals who have undergone kidney transplantation
Metformin use potentially causes lactic acidosis if contrast-induced nephropathy occurs, and European guidelines (ESUR) recommends stopping metformin at least 48 hours before a CT with IV contrast if GFR is between 30 and 44 ml/min/1.73 m2, unless emergent, and resume metformin 48 hours after the CT if renal function has not deteriorated. If lower, no contrast should be given unless absolutely necessary. In such cases, Swedish guidelines only include withholding metformin after the CT, and not before.
Other relative or absolute contraindications to IV contrast, regardless of GFR, are contrast allergy (see CT with IV contrast#Allergy) and untreated hyperthyroidism (see Iodinated contrast and hyperthyroidism).
How much contrast can be given?
In some emergent conditions such as CT of aortic aneurysm with suspected rupture, the need for contrast is greater than the risk of contrast-induced nephropathy.
For the rest of the investigations, evidence suggests that contrast doses should be limited to a ratio of grams of iodine to glomerular filtration rate (Igram / GFRml/min) of a maximum of 1 g/(ml/min). According to European guidelines, the ratio should be less than 1.1 g/(ml/min) for intra-arterial contrast medium administration with first-pass renal exposure (not passing lungs or peripheral tissue before reaching the kidneys). Swedish guidelines are more restrictive, recommending a ratio of less than 0.5 g/(ml/min) in patients with risk factors and irrespective of route of administration, and even more caution in first-pass renal exposure.
|Igram / GFRml/min
|240 mg/ml||350 mg/ml||370 mg/ml|
|0.5||2.1 ml *GFRml/min||1.4 ml *GFRml/min||1.4 ml *GFRml/min|
|1||4.2 ml *GFRml/min||2.9 ml *GFRml/min||2.7 ml *GFRml/min|
|1.1||4.6 ml *GFRml/min||3.1 ml *GFRml/min||3.0 ml *GFRml/min|
How much contrast is needed
The reality is a continuum, where a suboptimal amount of contrast increases the risk of missing or misdiagnosing findings. Still, following are examples given in the literature:
|300 mg/ml||350 mg/ml||370 mg/ml|
|CT of brain||95ml||80 ml||75 ml|
|CT of thorax||Overall||70 - 95 ml[notes 2]||60 - 80 ml[notes 2]||55 - 75 ml[notes 2]||Parenchymal changes of the lung can often be evaluated adequately without the use of intravenous contrast.|
|CT of pulmonary embolism||20 ml[notes 3]||17 ml[notes 3]||15 ml[notes 3]||Minimal amount when using specific low-contrast protocol.[notes 3]|
|CT of abdomen||Overall||70 ml||60 ml||55 ml|
|Liver||55 ml[notes 4]||45 ml[notes 4]||40-45 ml[notes 4]||Minimal required amount.[notes 4]|
|CT angiography||25 ml[notes 5]||20 ml[notes 5]||When using specific low-contrast protocol.[notes 5]|
Underweight or overweight?
At moderate weight deviations, corrections can be made by adjusting contrast dose proportionally to patient weight. Still, the needed dose is actually proportional to the lean body weight of the patient. For both men and women weighing more than about 85 kg,[notes 6] contrast dose is optimally calculated by the Boer formula, using height and weight of the patient. Taking this formula, the needed volume of IV contrast from the unadjusted volume given in the table above becomes:
- For men: Weight-adjusted volume = Unadjusted volume × ((0.00723 × W) + (0.00474 × H) − 0.341)
- For women: Weight-adjusted volume = Unadjusted volume × ((0.00583 × W) + (0.011 × H) − 1.12)
, where W is body weight in kilograms and H is body height in centimeters.
Still, it is generally enough to make a rough estimation of the needed contrast, since there are for example inherent standard deviations in the usage of creatinine or cystatin C in calculating GFR.
Treating risk factors
Risk factors can sometimes be treated or at least mitigated, especially if having suddenly appeared, such as a decreased renal function when it was previously normal. In such cases a common easily treated cause is dehydration.
Hydration should be done in patients with suspected dehydration (such as recent vomiting, diarrhea and/or diuretic use), and is done by drinking or by intravenous volume expander, either before or after contract administration. Hydration should be avoided otherwise.[notes 8]
Use low voltage protocols where appropriate. Also, in the elderly, consider increasing radiation dosage.
For exams with split bolus protocol, consider converting to a single bolus and instead using repeated imaging of the target area to include the phases of interest.
As a fictional example, an obese 50 year old male has undergone gastric bypass surgery two days before and has now developed abdominal pain and diarrhea. This is an indication for CT with IV (and oral) contrast. GFR is estimated to be 31 ml/min.
Medical records are checked for additional risk factors, finding diabetes, probable dehydration and anemia. The patient took metformin, but not since the day before surgery (3 days prior), and it should therefore not be a significant risk factor. Based on a ratio of maximum 1 g iodine/(ml/min of GFR) and a local iodine concentration of 350 mg/ml, the amount of IV contrast that can be given is:
- 2.9 ml * 31 = 90 ml
With the local iodine concentration being 350 mg/ml, the weight-unadjusted volume needed for the abdominal CT is estimated to be 60 ml. The patient weights 120 kg and is 176 cm tall. The weight adjusted volume is thus:
- 60ml × ((0.00723 × 120) + (0.00474 × 176) − 0.341) = 82 ml
The contrast that can be given is thus slightly more than what is needed, and it is therefore acceptable to perform the CT with the estimated dose of IV contrast that is needed. At the same time, the patient had additional risk factors in the form of diabetes and probable anemia, and the low GFR was probably resulting from dehydration because of the diarrhea. It is therefore more appropriate to treat this risk factor by rehydrating him before the exam if time allows. In an emergency, the patient may need surgery without a prior CT.
- For a full list of contributors, see article Radlines:Authorship for details. . Creators of images are attributed at the image description pages, seen by clicking on the images. See
- 0.3–0.4 gI/kg in a 70kg individual, according to:
- Iezzi, Roberto; Larici, Anna Rita; Franchi, Paola; Marano, Riccardo; Magarelli, Nicola; Posa, Alessandro; Merlino, Biagio; Manfredi, Riccardo; et al. (2017). "Tailoring protocols for chest CT applications: when and how?
- Using dual energy CTA (such as 90/150SnkVp), according to:
- Leroyer, Christophe; Meier, Andreas; Higashigaito, Kai; Martini, Katharina; Wurnig, Moritz; Seifert, Burkhardt; Keller, Dagmar; Frauenfelder, Thomas; et al. (2016). "Dual Energy CT Pulmonary Angiography with 6g Iodine—A Propensity Score-Matched Study
- The liver generally needs an enhancement of at least 30 HU for proper evaluation according to:
- Multislice CT
- Bae, Kyongtae T. (2010). "Intravenous Contrast Medium Administration and Scan Timing at CT: Considerations and Approaches
- CT-angiography in a 70kg person, with 100-150 mg I/kg by using 80 kVp, mAs-compensation for constant CNR, fixed injection duration adapted to scan time, automatic bolus tracking and a saline chaser, according to:
- Nyman, Ulf (2012). Contrast Medium-Induced Nephropathy (CIN) Gram-Iodine/GFR Ratio to Predict CIN and Strategies to Reduce Contrast Medium Doses
- At above this weight, calculated contrast amount with the Boer formula deviates more than 10% from both the weight-unadjusted amount, as well as the amount taken proportionally to the weight, for both men and women.
- 176 cm male and 162 cm female
- Hydration of people with low renal function, without separating dehydrated from non-dehydrated individuals, seems to only increase complication rates, including electrolyte imbalances and cardiac arrhythmias:
Nijssen, Estelle C; Rennenberg, Roger J; Nelemans, Patty J; Essers, Brigitte A; Janssen, Marga M; Vermeeren, Marja A; Ommen, Vincent van; Wildberger, Joachim E (2017). "Prophylactic hydration to protect renal function from intravascular iodinated contrast material in patients at high risk of contrast-induced nephropathy (AMACING): a prospective, randomised, phase 3, controlled, open-label, non-inferiority trial ". The Lancet 389 (10076): 1312–1322. doi:10.1016/S0140-6736(17)30057-0. ISSN 01406736.
- Rudnick, M.; Feldman, H. (2008). "Contrast-Induced Nephropathy: What Are the True Clinical Consequences? ". Clinical Journal of the American Society of Nephrology 3 (1): 263–272. doi:10.2215/CJN.03690907. ISSN 1555-9041.
- Nyman, Ulf; Ahlkvist, Joanna; Aspelin, Peter; Brismar, Torkel; Frid, Anders; Hellström, Mikael; Liss, Per; Sterner, Gunnar; et al. (2018). "Preventing contrast medium-induced acute kidney injury ". European Radiology. doi:10.1007/s00330-018-5678-6. ISSN 0938-7994.
- Kalgi Modi, Scott C. Dulebohn (2017). Contrast-Induced Nephropathy. StatPearls Publishing. CC-BY-4.0
- . Iodine-based contrast media. ESUR. Retrieved on 2018-11-09.
- . [file:///C:/Users/mikha19/Downloads/Nationella_rek_metformin_kontrastmedel_v61_2018-05-07.pdf Nationella rekommendationer: Svensk uroradiologisk förenings kontrastmedelsgrupp: METFORMIN. Version 6.1] (2018-05-07).
- Keaney, J. J.; Hannon, C. M.; Murray, P. T. (2013). "Contrast-induced acute kidney injury: how much contrast is safe? ". Nephrology Dialysis Transplantation 28 (6): 1376–1383. doi:10.1093/ndt/gfs602. ISSN 0931-0509.
- . New Zealand Datasheet. New Zealand Medicines and Medical Devices Safety Authority. Retrieved on 2018-10-16.
- Caruso, Damiano; De Santis, Domenico; Rivosecchi, Flaminia; Zerunian, Marta; Panvini, Nicola; Montesano, Marta; Biondi, Tommaso; Bellini, Davide; et al. (2018). "Lean Body Weight-Tailored Iodinated Contrast Injection in Obese Patient: Boer versus James Formula ". BioMed Research International 2018: 1–6. doi:10.1155/2018/8521893. ISSN 2314-6133.
- Levine, Marc S.; Carucci, Laura R. (2014). "Imaging of Bariatric Surgery: Normal Anatomy and Postoperative Complications ". Radiology 270 (2): 327–341. doi:10.1148/radiol.13122520. ISSN 0033-8419.