What Is Low Blood Creatinine and How Is It Treated?

Blood urea nitrogen (BUN) and creatinine tests are blood tests performed as part of routine health screenings. These tests help evaluate how well your kidneys are working. If your doctor suspects a kidney problem, you will be advised to have BUN tests.

A high BUN/creatinine ratio may be caused by conditions that reduce blood flow to the kidneys. BUN measures the amount of urea in your blood. Urea nitrogen is a waste product formed when your liver breaks down the proteins in the food you eat; this protein breakdown produces BUN. Normally, BUN is removed by your kidneys. If your kidneys are not working properly, BUN builds up, causing BUN levels to rise. While BUN levels can fluctuate, blood creatinine levels mostly remain stable. Creatinine is a waste product resulting from normal muscle wear and tear. It is produced from creatine, a protein that helps generate energy for muscle contractions. Creatinine is eliminated from the body by the kidneys. When kidney function is abnormal, creatinine levels in the blood rise.

What Is the BUN/Creatinine Ratio?

The BUN/creatinine ratio is the concentration of BUN relative to creatinine in the blood. It is used to check for health problems such as dehydration, kidney disease, intestinal bleeding and other conditions.

What Causes a High BUN/Creatinine Ratio?

The normal BUN/creatinine ratio is between 10:1 and 20:1. Typically, normal BUN and creatinine levels result in a normal BUN/creatinine ratio, and only a change in one value or the other will produce an abnormal ratio. However, high BUN and creatinine values will still give a normal ratio if they rise at the same rate, which is why all three values are important for diagnosis.

A high BUN/creatinine ratio in your blood tests can have three causes: high BUN with normal creatinine, normal BUN with low creatinine, or both BUN and creatinine being high but BUN disproportionately so. On the other hand, a low BUN/creatinine ratio may result from low BUN with normal creatinine, normal BUN with high creatinine, or both values being low with BUN proportionally lower than creatinine.

A high BUN/creatinine ratio can be caused by conditions that reduce blood flow to the kidneys, such as congestive heart failure or dehydration. BUN/creatinine ratios can also increase with age and with loss of muscle mass. Abnormal BUN and creatinine levels are caused by underlying diseases and usually appear together with the symptoms of the disease.

A high BUN/creatinine ratio can be caused by conditions that reduce blood flow to the kidneys, such as congestive heart failure or dehydration.

Causes of a high BUN/creatinine ratio include:

• Dehydration: Raises both BUN and creatinine, but raises BUN more.
• Intestinal bleeding: Blood loss reduces the blood volume and circulation reaching the kidneys, increasing BUN. In addition, the protein-rich blood in the intestine is difficult to digest.
• Hyperthyroidism: Increases BUN and lowers creatinine levels.
• Congestive heart failure: Increases urea reabsorption in the kidneys, causing BUN to rise.
• Kidney diseases: These can raise both BUN and creatinine.
• Medications: Some antibiotics such as tetracycline, and corticosteroids used to treat inflammation, can increase the BUN/creatinine ratio.

Causes of a low BUN/creatinine ratio include:

• Malnutrition and low protein intake: Low protein intake reduces BUN production.
• Hypothyroidism: Increases creatinine levels.
• Advanced liver disease: The liver cannot break down protein to produce urea, so BUN falls.
• Sickle cell anemia: The kidneys reabsorb very little urea and it is excreted in the urine, lowering BUN.
• Rhabdomyolysis: A condition caused by the rapid breakdown of muscle, in which creatinine levels rise.
• Kidney damage: The kidneys cannot filter creatinine effectively, and blood creatinine levels rise.
• Medications: Some medications, including acetazolamide and diuretics used for conditions such as glaucoma, altitude sickness and heart failure, can alter BUN levels.

What Factors Increase or Decrease Creatinine Levels?

Many conditions can increase or decrease the BUN/creatinine ratio. If you have been diagnosed with an abnormal BUN/creatinine ratio, treating the underlying condition should usually bring the balance back to normal. In addition to treating your condition, your doctor may suggest ways to change your BUN and/or creatinine levels.

Factors that affect BUN and creatine levels include:

• Factors that increase BUN
  • If your BUN is low, increase your dietary protein with beans or lean meats
  • Avoid or limit alcohol consumption, which can raise BUN
• Factors that decrease BUN
  • Adequate fluid intake can lower BUN
  • Obesity and a high BMI, which can cause kidney dysfunction, lead to low BUN
• Factors that decrease creatinine
  • Avoiding creatine and creatine-based foods
  • Increased dietary fiber
  • Weight loss, which can improve kidney health
• Factors that increase creatinine
  • Increased exercise and physical activity
  • Increased dietary intake of creatinine