BUNcreatinine

BUNcreatinine, more commonly referred to as the BUN/creatinine ratio, is a combined measure used in clinical practice to help assess kidney function and to interpret abnormalities in blood urea nitrogen (BUN) and creatinine levels. BUN reflects the amount of nitrogen in the blood in the form of urea, a waste product produced in the liver from protein metabolism and cleared by the kidneys. Creatinine is a breakdown product of creatine in muscle, produced at a relatively constant rate and freely filtered by the kidneys. Together, these two markers provide information about renal filtration and overall kidney function.

The BUN/creatinine ratio is calculated by dividing the BUN value by the creatinine value. In adults, a typical normal range is roughly 10:1 to 20:1, though exact values depend on laboratory methods. A high ratio (often >20:1) can suggest prerenal azotemia due to reduced renal perfusion from dehydration, heart failure, or significant volume loss; it can also be influenced by high protein intake or GI bleeding. A normal or low ratio with a rising creatinine may indicate intrinsic renal disease or reduced creatinine production. It is important to note that the ratio is not diagnostic on its own and must be interpreted alongside other clinical data and tests.

Clinical use includes evaluating acute kidney injury, chronic kidney disease, and hydration status, as well as monitoring therapy. Creatinine-based estimates of glomerular filtration rate (eGFR) are commonly used to stage kidney disease, but BUN and the ratio remain helpful supplementary measures. Limitations include variation with age, sex, muscle mass, diet, liver function, and certain medications.