urea nitrogen (BUN)/creatinine ratio

Introduction

The ratio to serum urea nitrogen to serum creatinine used to assess hydration status.

Clinical significance

• a value of > 20 suggests prerenal azotemia

Notes

• Acute or chronic renal failure is the most common cause of high BUN levels.
• In prerenal failure, a low renal blood supply, such as occurs with hypovolemia or congestive heart failure, leads to reduced glomerular filtration & therefore an elevated BUN.
• In renal failure, damage to the nephrons, particularly such as occurs with glomerulonephritis or pyelonephritis, leads to decreased glomerular filtration & excretion.
• Blood urea nitrogen begins to rise when the glomerular filtration rate (GFR) falls below 50 mL/min due to increased resorption of urea in the proximal tubules (the normal GFR in an average size manis approximately 125 mL/min).
• The BUN/creatinine ratio increases as well (> 20).

More general terms

• urine creatinine ratio