Final Word The BUN and creatinine are both end products of metabolism. The BUN and creatinine are waste products that need to be filtered by the kidneys and excreted through urination. A small amount of BUN and creatinine may be present in the blood and are just normal. However, if the ratios are too high or too low, it could signal that there is something wrong in your kidneys and liver. A high BUN and creatinine ratio could indicate a possible kidney-related problem.
BUN/Creatinine 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.
| Bun/Creatinine Ratio | 6-22 (calc) | ||||
| Urea Nitrogen (BUN) | |||||
| Age | Male (mg/dL) | Female (mg/dL) | |||
| 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.
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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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What Causes a High BUN Creatinine Ratio?
The normal ratio of BUN to creatinine is between 10:1 and 20:1. A high BUN to creatinine ratio may be due to conditions that lead to decreased blood flow to the kidneys, such as congestive heart failure or dehydration.
BUN to creatinine ratios can increase with both age and muscle mass.
What is a BUN creatinine ratio?
Blood urea nitrogen (BUN) and creatinine tests are blood tests that are performed as part of routine health screening. These tests help assess how well your kidneys are functioning. If your doctor suspects any kidney conditions, then the doctor will advise you to go for BUN tests.
BUN
BUN measures the amount of urea in your blood. Urea nitrogen is the waste product that is formed as your liver breaks down the proteins in foods you eat; this protein breakdown creates BUN.
Usually, BUN is removed by your kidneys. If your kidneys are not functioning properly, the BUN gets stored, resulting in increased BUN levels.
Creatinine
While BUN levels may vary, creatinine blood levels are mostly stable. Creatinine is a waste product that is formed as a result of muscle wear and tear. Creatinine is produced from creatine, a protein that helps produce energy for muscle contractions.
Creatinine is removed from the body by the kidneys. When there is an abnormal function of the kidneys, creatinine levels increase in the blood.
A BUN to creatinine ratio is used to check the health issues such as dehydration, kidney diseases, intestinal bleeding, and other conditions.
What causes abnormal BUN creatinine levels?
Abnormal BUN to creatinine levels are due to the underlying diseases and typically accompanied by the symptoms of the underlying conditions.
Causes of high BUN to creatinine levels include:
- Dehydration
- Intestinal bleeding
- Hyperthyroidism
- Congestive heart failure
- Kidney diseases
- Medications such as tetracycline and corticosteroids
Causes of low BUN to creatinine levels include:
- Malnutrition, with low protein intake
- Hyperthyroidism
- Advanced liver diseases (the liver cannot produce enough urea)
- Sickle cell anemia (kidneys absorb too little urea)
- Rhabdomyolysis (muscles break down rapidly)
- Kidney damage
- Medications such as acetazolamide and diuretics for conditions such as glaucoma, altitude sickness, and heart failure
What factors can increase or decrease BUN creatinine ratio?
Factors that increase BUN
- Increased dietary protein
- Alcohol consumption
Factors that reduce BUN
- Proper hydration
- Obesity and high BMI (which can cause kidney dysfunction)
Factors that reduce creatinine
- Not consuming creatinine and creatine-based food
- Increased dietary fiber
- Weight loss, which can improve kidney health
Factors that increase creatinine
- Increased exercise and physical activity
- Avoiding alcohol
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References
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What Is the Purpose of Urea?
Urea is a nitrogenous waste product that is produced in the body. The liver breaks down protein and ammonia to make urea. Further, it is taken up by the kidneys. The kidneys filter the blood and transfer the urea from the blood to the urine. Thus, urea serves the purpose of expelling extra nitrogen and nitrogenous products from the body.
BUN/Creatinine Ratio Understand (High vs. Low Levels, Normal Range)
A BUN creatinine ratio is a blood work done to detect acute or chronic renal disease/failure.
Both BUN and creatinine are filtered in the kidneys and excreted through urination and they are a perfect parameter for identifying the overall functions of the kidneys. (1, 2)
Image 1: The standard unit of measurements for BUN and creatinine.
Picture Source: lifeinthefastlane.com
Understanding the difference between BUN and creatinine test and their relationship
BUN Test
BUN stands for Blood Urea Nitrogen. The BUN test measures the level of nitrogen in the blood.
Doctors order this test to assess the functions of the kidneys and liver.
Nitrogen is urea’s waste product. The function of the kidneys is to filter the urea so that waste products will be removed from the body through urination.
The liver continuously produces urea and so it is just normal to have a small amount of urea in the blood. If the urea in the blood is abnormally high, it is an indicator that the kidneys are not functioning well.
There could be something wrong with your kidneys that need to be addressed properly and timely. (1, 2, 3)
Creatinine Test
A creatinine is a molecule produced by muscle metabolism. It is transported through the bloodstream and filtered in the kidneys and excreted through the urine.
The muscle mass of a person defines the rate of creatinine formation. Ideally, the level of creatinine remains constant throughout the day.
If the level of creatinine is high, then it indicates that there is something wrong with your kidneys. (3, 4)
Picture 2: BUN and creatinine ratio is measured using the above formula.
Photo Source: www.labpedia.net
What is a BUN creatinine ratio and its significance?
The BUN and creatinine test results are combined by the doctor to determine the BUN to creatinine ratio.
This is to find out the functions and overall condition of the liver and kidneys. It is used by the doctor in formulating an accurate diagnosis of health problems that have something to do with the kidneys.
Other reasons for taking BUN to creatinine ratio test include the following:
- Evaluate the functions of the kidneys
- Diagnose kidney-related diseases such as acute and/or chronic renal disease and urinary tract blockages
- Monitor the effectiveness of the treatments related to kidney problems
- It helps in diagnosing gastrointestinal bleeding
- It is useful in diagnosing severe dehydration (causes the BUN level to rise) (2, 3, 4, 5)
What can cause a high bun creatinine ratio?
- Congestive heart failure
- Urinary tract obstruction
- Gastrointestinal bleeding
- Trauma (5, 6)
What can cause a low BUN creatinine ratio?
- Liver-related diseases
- Low protein diet
- Severe polyuria and polydipsia
- Diabetes mellitus
- Cushing’s disease (6, 7)
What can cause an increase creatinine with normal BUN level?
- Severe muscle trauma
- Acute myositis
- Too much intake of ascorbic acid (vitamin C)
- Intake of cephalosporins (7)
What can cause a high BUN and normal creatinine?
- Gastrointestinal hemorrhage
- High protein diet
- Fever
- Intake of corticosteroids or tetracyclines (8, 9)
What can cause a low creatinine and normal BUN?
- Decrease muscle mass
- Severe cachexia (9, 10)
What to keep in mind before undergoing a BUN creatinine ratio test?
Your protein intake can significantly affect the test result. A high protein intake may cause an abnormally high level of BUN. On the other hand, a low protein intake may lead to an abnormally low level of BUN.
If you are going to undertake a BUN creatinine ratio test, make sure that you consume a normal amount of protein and that you are properly hydrated.
That way, you will be able to come up with an accurate BUN creatinine ratio test result. The result can also be affected by pregnancy. (2, 5, 8, 9)
“Click on image for the calculator”
Photo 3: A blood sample is drawn from the patient’s arm and sent immediately to the lab for testing and evaluation.
Image Source: lh3.googleusercontent.com
Image 4: BUN and creatinine are two parameters used to detect the condition of the kidneys.
Picture Source: i.ytimg.com
How is the test taken?
The procedure is performed by a lab technician. A blood is drawn from your upper arm using a sterile needle. The entire process would take around 5 to 10 minutes depending on the visibility of your vein.
What is a normal BUN and creatinine level ratio?
To get the BUN creatinine ratio, the BUN count is divided by the creatinine count.
What is the normal BUN creatinine ratio?
The ideal ratio is between 10:1 and 20:1. If the result is higher than the numbers mentioned, it indicates that there is a high level of BUN in the blood.
It is linked with kidney-related diseases or decreased flow of blood to the kidneys secondary to dehydration or congestive heart failure. If the result is below the normal ratio, then it could indicate malnutrition or liver-related diseases. (3, 6, 9, 10)
Final Word
The BUN and creatinine are both end products of metabolism. The BUN and creatinine are waste products that need to be filtered by the kidneys and excreted through urination.
A small amount of BUN and creatinine may be present in the blood and are just normal. However, if the ratios are too high or too low, it could signal that there is something wrong in your kidneys and liver.
A high BUN and creatinine ratio could indicate a possible kidney-related problem.
References:
- https://en.wikipedia.org/wiki/BUN-to-creatinine_ratio
- https://www.questdiagnostics.com/testcenter/TestDetail.action?ntc=296
- https://www.sciencedirect.com/topics/medicine-and-dentistry/bun-to-creatinine-ratio
- https://www.healthlabs.com/bun-creatinine-ratio-testing
- https://acutecaretesting.org/en/articles/urea-and-creatinine-concentration-the-urea-creatinine-ratio
- https://lifeinthefastlane.com/ccc/ureacreatinine-ratio/
- https://www.ahajournals.org/doi/abs/10.1161/circheartfailure.112.968230
- https://www.mayoclinic.org/tests-procedures/blood-urea-nitrogen/about/pac-20384821
- https://www.selfhacked.com/blog/bun-creatinine-ratio-high-low-levels-normal-range/
- https://www.beaumontlaboratory.com/test-lab-directory/lab-test-details/?testid=1305
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