Dr. Diana Rangaves, PharmD

What are the Causes of a High BUN-Creatinine Ratio?

BUN-creatinine ratio: Creatinine and blood urea nitrogen (BUN) are essential biomarkers that offer crucial insights into your kidney function and overall body health. BUN is the amount of nitrogen (from urea) in your blood. It is a waste product created when the liver breaks down proteins. On the other hand, creatinine is a byproduct of metabolism in your muscles.

Your kidney filters these substances from your blood and eliminate them through urine. If your kidney function declines or you have other health issues, the levels of BUN and creatinine in your blood change. Thus, they’re crucial indicators of kidney health and different metabolic processes in your body.

Common Causes of High BUN/Creatinine Ratio

The normal BUN-creatinine ratio is between 10:1 and 20:1. Normal creatinine and normal BUN levels will result in the recommended BUN/creatinine levels. Any significant changes to the levels of any of these biomarkers in your body may lead to an abnormal ratio.

However, if BUN and creatinine levels increase in the same proportion, they’ll still result in a normal ratio as long as it doesn’t exceed 20:1. Therefore, the three values are crucial for assessing kidney health. Here are the causes of a high ratio:

Dehydration & Volume Depletion

When you are dehydrated, your kidneys increase the concentration of urine to conserve water. This can lead to higher reabsorption of urea (which rises BUN) while the excretion of creatinine remains unchanged. High BUN can result in a disproportionate increase in the ratio.

Gastrointestinal Bleeding

If you have upper gastrointestinal bleeding, the blood will enter your digestive tract. The proteins from your red blood cells will be broken down and absorbed. This can lead to increased urea production and increase the BUN levels while creatinine levels remain unchanged. This can cause a dangerously high ratio of BUN to creatinine, like 30:1 or even 40:1. 

Other Medical Conditions.

Some medical conditions can increase the BUN/creatinine ratio. These include;

  • Heart failure can reduce kidney perfusion, which elevates the BUN-creatinine levels
  • Any form of shock can lower blood flow to the kidneys and affect the ratio
  • High protein diet or increased breakdown of protein
  • Some medications, such as tetracyclines, corticosteroids, or excessive diuretics
  • Advanced liver disease affects urea production

Note that a BUN to creatinine ratio that exceeds 30:1 is considered dangerously high. Such levels may indicate serious underlying health issues that necessitate immediate medical attention.

The Clinical Significance of BUN/Creatinine Ratio.

Doctors or healthcare providers use the BUN to creatinine ratio and other clinical findings to differentiate some health conditions from others. If your elevated ratio has normal creatinine, it suggests pre-renal causes. On the other hand, if your high ratio has elevated creatinine, it may indicate post-renal obstruction.