Contrast-induced nephropathy

Contrast-induced nephropathy is a form of kidney damage in which there has been recent exposure to medical imaging contrast material without another clear cause for the acute kidney injury. CIN is classically defined as a serum creatinine increase of at least 25% and/or an absolute increase in serum creatinine of 0.5 mg/dL after using iodine contrast agent without another clear cause for acute kidney injury, but other definitions have also been used. Contrast-induced nephropathy is a form of kidney damage in which there has been recent exposure to medical imaging contrast material without another clear cause for the acute kidney injury. CIN is classically defined as a serum creatinine increase of at least 25% and/or an absolute increase in serum creatinine of 0.5 mg/dL after using iodine contrast agent without another clear cause for acute kidney injury, but other definitions have also been used. Despite extensive speculation, the actual occurrence of contrast-induced nephropathy has not been demonstrated in the literature. The mechanism of contrast-induced nephropathy is not entirely understood, but is thought to include direct damage from reactive oxygen species, contrast-induced increase in urine output, increased oxygen consumption, changes in dilation and narrowing of the blood vessels to the kidneys, and changes in urine viscosity. Analysis of observational studies has shown that radiocontrast use in CT scanning is not causally related to changes in kidney function. Given the increasing doubts about the contribution of radiocontrast to acute kidney injury, the American College of Radiology has proposed the name postcontrast acute kidney injury which does not imply a causal role, with CIN reserved for the rare cases where radiocontrast is likely to be causally related. There are multiple risk factors of contrast-induced nephropathy, whereof a review in 2016 emphasized chronic kidney disease, diabetes mellitus, high blood pressure, reduced intravascular volume, and/or old age. European guidelines classify a pre-existing decreased renal function to be a risk factor of contrast-induced nephropathy in the following cases: To calculate estimated GFR from creatinine, European guidelines use the CKD-EPI formula in adults ≥ 18 years, and the revised Schwartz formula in children. 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. The Roxana Mehran score is a clinical prediction rule to estimate probability of nephropathy (increase ≥25% and/or ≥0.5 mg/dl in serum creatinine at 48 h):