Contrast-induced nephropathy

European guidelines classify a pre-existing decreased kidney function to be a risk factor of contrast-induced nephropathy in the following cases:[5]

• Estimated glomerular filtration rate (eGFR) < 45 ml/min/1.73 m² of body surface area before intra-arterial administration with first-pass renal exposure (not passing lungs or peripheral circulation before kidneys), or in the intensive care unit
• eGFR < 30 ml/min/1.73 m2 before intravenous administration or intra-arterial administration with second-pass renal exposure
• Known or suspected acute kidney injury

To calculate estimated GFR from creatinine, European guidelines use the CKD-EPI formula in adults ≥ 18 years, and the revised Schwartz formula in children.[5] Swedish guidelines recommends no specific formula in children because of lack of evidence, but on the other hand recommends GFR based on cystatin C rather than creatinine in those with abnormal muscle mass or liver failure or cirrhosis.[5]

The Mehran score is a clinical prediction rule to estimate probability of CIN which includes the following risk factors: systolic blood pressure <80 mm Hg for at least one hour requiring inotropic support, intra-arterial balloon pump, congestive heart failure with NYHA class III or worse, history of pulmonary edema, age >75 years, hematocrit level <39% for men and <35% for women, diabetes mellitus, contrast media volume, decreased kidney function (serum creatinine level >1.5 g/dL or decreased estimated glomerular filtration rate).[6][7]

European guidelines include the following procedure-related risk factors:[5]

• Large doses of contrast given intra-arterially with first-pass renal exposure
• Use of contrast agents with high osmolality (limited use today)
• Multiple contrast injections within 48–72 h. Swedish guidelines also include gadolinium MRI contrast agents in this aspect.

Swedish guidelines list the following additional risk factors:[5]

• Hypoxia
• Cirrhosis
• NSAID or nephrotoxic medication
• Individuals on dialysis with residual renal function of at least 400 ml urine/24h
• Individuals having undergone kidney transplantation

According to European guidelines, the ratio of the contrast dose (in grams of iodine) divided by the absolute estimated glomerular filtration rate (GFR) 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).[5] 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.[5]

Hydration by drinking or intravenous volume expander, either before or after contrast administration, decreases the risk of contrast-induced nephropathy.[8] Evidence also supports the use of N-acetylcysteine with intravenous saline among those getting low molecular weight contrast.[9] The use of statins with N-acetylcysteine and intravenous saline is also supported.[9]

• Oral hydration may be as effective as the intravenous route for volume expansion to prevent contrast-induced nephropathy, according to a review in 2013.[8]
• Adenosine antagonists such as the methylxanthines theophylline and aminophylline, may help[10] although studies have conflicting results.[11]
• N-acetylcysteine (NAC) by mouth twice a day, on the day before and of the procedure if creatinine clearance is estimated to be less than 60 mL/min [1.00 mL/s]) may reduce risk. Some authors believe the benefit is not overwhelming.[12] A systematic review concluded that NAC is "likely to be beneficial" but did not recommend a specific dose.[13]
• Ascorbic acid may be protective against CIN, according to a systematic review of randomized controlled trials.[14]
• Matched hydration, meaning infusion of a volume of normal saline equal to the urine output, has been found to reduce kidney injury, dialysis, adverse events and mortality compared to standard therapy.[15][16]