From the Guidelines
The BUN to creatinine ratio is not a reliable indicator of kidney function, as BUN can be influenced by factors such as hydration status, protein intake, and liver disease, while creatinine is more directly related to kidney filtration capacity. When evaluating kidney function, it is more accurate to use the weekly renal Kt/Vurea, which takes into account the urea clearance normalized to total body water, as recommended by the NKF-K/DOQI Clinical Practice Guidelines for Peritoneal Dialysis Adequacy 1. The BUN to creatinine ratio can be misleading, as a low BUN may be seen in patients with low protein intake or liver disease, while a low creatinine may be seen in patients with decreased muscle mass, such as the elderly or malnourished patients 1. Some key points to consider when evaluating kidney function include:
- The weekly renal Kt/Vurea should be used to monitor progression of kidney failure, rather than relying on BUN and creatinine values alone 1
- A weekly Krt/Vurea of 2.0 approximates a renal urea clearance of 7 mL/min and a renal creatinine clearance of 9-14 mL/min/1.73 m2 1
- The estimation of total body water (V) is crucial in calculating Kt/Vurea, but its estimation by formulae has not been validated in children with renal failure 1. It is essential to interpret the BUN to creatinine ratio in the context of the patient's clinical presentation, taking into account factors such as hydration status, protein intake, and liver disease, rather than relying solely on this ratio to assess kidney function.
From the Research
BUN Creatinine Ratio
The BUN (Blood Urea Nitrogen) creatinine ratio is a diagnostic tool used to evaluate kidney function and distinguish between prerenal, renal, and postrenal causes of acute kidney injury [(2,3,4)].
- Prerenal causes: A high BUN creatinine ratio may indicate prerenal causes of acute kidney injury, such as dehydration, heart failure, or liver disease [(2,3)].
- Renal causes: A normal or low BUN creatinine ratio may indicate renal causes of acute kidney injury, such as glomerulonephritis or tubulointerstitial disease [(3,4)].
- Postrenal causes: A normal or low BUN creatinine ratio may also indicate postrenal causes of acute kidney injury, such as urinary tract obstruction [(3,4)].
Kidney Function and Heart Failure
The BUN creatinine ratio can also provide insight into the relationship between kidney function and heart failure [(2,3,4)].
- Heart failure and kidney dysfunction: Heart failure is often associated with kidney dysfunction, and the BUN creatinine ratio can help evaluate the severity of kidney impairment in patients with heart failure [(2,3)].
- Mortality risk: A low estimated glomerular filtration rate (eGFR) is associated with a higher risk of mortality in patients with heart failure, and the BUN creatinine ratio can help identify patients at high risk 4.