BUN Creatinine Ratio Calculator

The BUN creatinine ratio compares blood urea nitrogen with serum creatinine, two waste-related measurements commonly included in metabolic and kidney panels. BUN reflects nitrogen produced when the body breaks down protein. The liver converts this nitrogen to urea, which travels through the blood and is removed mainly by the kidneys. Creatinine is produced from normal muscle metabolism and is also filtered by the kidneys. Dividing BUN in mg/dL by creatinine in mg/dL gives the conventional ratio. A frequently cited adult reference range is about 10:1 to 20:1, but laboratories, populations, and clinical circumstances vary. A ratio above that interval can occur when urea rises disproportionately, as may happen with reduced blood flow to the kidneys, dehydration, gastrointestinal bleeding, high protein intake, tissue breakdown, or some medicines. A lower ratio can be associated with reduced urea production, low protein intake, severe liver dysfunction, fluid excess, or a proportionally greater creatinine concentration. These patterns are not diagnoses and have many exceptions. The ratio must be interpreted with the individual BUN and creatinine values, estimated glomerular filtration rate, electrolytes, urine findings, symptoms, medical history, and volume status. For example, a ratio can look typical even when both laboratory values are elevated. Muscle mass can influence creatinine, while diet, liver function, catabolic state, and hydration can influence BUN. Unit conventions also matter. This calculator assumes both entries use mg/dL; values reported in mmol/L or micromol/L require conversion before using this conventional ratio. Use results from the same blood collection and compare them with the reference intervals printed by the performing laboratory. Do not use the ratio alone to label prerenal, intrinsic renal, or postrenal disease. New kidney abnormalities, reduced urine output, swelling, confusion, vomiting, or significant dehydration warrant prompt professional assessment. A healthcare professional can evaluate trends and determine whether repeat testing, urine studies, imaging, medication review, or treatment is appropriate.