Kidney Health

BUN/Creatinine Ratio

Optimal Result: 9 - 20 :1 ratio.

The principle behind this ratio is the fact that both urea (BUN) and creatinine are freely filtered by the glomerulus; however, urea reabsorbed by the tubules can be regulated (increased or decreased) whereas creatinine reabsorption remains the same (minimal reabsorption).

The BUN/Creatinine ratio is useful in the differential diagnosis of acute or chronic renal disease. Reduced renal perfusion, e.g., congestive heart failure, or recent onset of urinary tract obstruction will result in an increase in BUN/Creatinine ratio. Increased urea formation also results in an increase in the ratio, e.g., gastrointestinal bleeding, trauma, etc. When there is decreased formation of urea as seen in liver disease, there is a decrease in the BUN/Creatinine ratio. In most cases of chronic renal disease the ratio remains relatively normal.

Reference Range(s):

Bun/Creatinine Ratio 6-22 (calc)  
Urea Nitrogen (BUN)    
Age Male (mg/dL) Female (mg/dL)
<1 Month 4-12 3-17
1-11 Months 2-13 4-14
1-3 Years 3-12 3-14
4-19 Years 7-20 7-20
≥20 Years 7-25 7-25
Creatinine    
Age Male (mg/dL) Female (mg/dL)
≤2 days 0.79-1.58 0.79-1.58
3-27 days 0.35-1.23 0.35-1.23
1 month-9 years 0.20-0.73 0.20-0.73
10-12 years 0.30-0.78 0.30-0.78
13-15 years 0.40-1.05 0.40-1.00
16-17 years 0.60-1.20 0.50-1.00
18-19 years 0.60-1.26 0.50-1.00
20-49 years 0.60-1.35 0.50-1.10
50-59 years 0.70-1.33 0.50-1.05
60-69 years 0.70-1.25 0.50-0.99
70-79 years 0.70-1.18 0.60-0.93
≥80 years 0.70-1.11 0.60-0.88

For patients >49 years of age, the upper reference limit for creatinine is approximately 13% higher for people identified as African-American.

What does it mean if your BUN/Creatinine Ratio result is too low?

A decreased ratio may be observed with liver disease and poor diet. Temporary levels that are high or low may not be a cause for concern and should be retested to confirm.

What does it mean if your BUN/Creatinine Ratio result is too high?

An increased ratio of BUN to creatinine may be due to conditions that cause a decrease in the flow of blood to the kidneys, such as congestive heart failure or dehydration. It may also be seen with high protein blood levels or from gastrointestinal bleeding.

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