According to "Conn's Current Therapy 2010," acute tubular necrosis can result due to the effects of computed tomography, or CT, contrast material. Acute tubular necrosis is a condition where the kidneys begin to fail at a rapid rate and the urine becomes a muddy brown color because of the dying of kidney tubular cells. Physicians monitor kidney function by the concentrations of urea nitrogen and creatinine in the blood. The levels of these byproducts within your blood is a good indicator that your kidneys are able to tolerate the contrast.
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Blood urea nitrogen is a waste product of the breakdown of proteins in your body that the kidney normally filters and excretes, according to "Harrison's Principles of Internal Medicine." Normal concentrations of BUN in an adult fall between 8 and 25 milligrams per decaliter, mg/dL. A BUN greater than 25 mg/dL indicates renal failure which is a contraindication for contrast medias used in medical imaging.
An article published in "Advances for Imaging & Radiation Oncology" explains that creatinine comes from the diet as well as the metabolism of a skeletal muscle organic acid called creatine. The filtration of creatinine is one of the most important markers of kidney function. Normal creatinine levels fall below 1.3 mg/dL. Levels greater than 2.0 are contraindications for CT contrast.
BUN to Creatinine Ratio
The book "Brenner and Rector's the Kidney" indicates that practitioners prefer to see BUN-to-creatinine ratios of less than 20 to 1 before administering CT contrast material. Ratio elevations greater than 20:1 are indicative of prerenal azotemia and may lead to acute tubular necrosis if contrast is applied. Under most circumstances, elevated BUN:Cr ratios are due to dehydration, which is a risk factor for contrast renal toxicity.