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BUN Creatinine Ratio

BUN Creatinine Ratio

Knowing the BUN creatinine ratio can help diagnose kidney problems. This article throws some light on BUN, creatinine, and the BUN creatinine ratio. Read on...
Mayuri Kulkarni
Last Updated: Apr 22, 2018
Blood tests are some of the most useful medical tests that help in the diagnosis of a myriad of health problems. The BUN creatinine ratio test is one such blood test that helps in detecting kidney problems. BUN (Blood Urea Nitrogen) and creatinine are two compounds found in the blood and the amount of these substances is directly governed by the functioning of the kidneys. Any dysfunction of the kidneys can increase or decrease the quantity of these compounds in the blood, and hence BUN-to-creatinine ratio is considered a reliable test to determine kidney problems. Before knowing more about the BUN creatinine ratio, let us understand what exactly is BUN and creatinine.
BUN and Creatinine
Blood Urea Nitrogen (BUN) can be defined as the amount of urea nitrogen present in the blood. Urea is a waste product formed in our body during the breakdown of proteins. During protein metabolism, the protein is converted into amino acids and these are further catabolized to ammonia. Urea is nothing but a substance formed by several molecules of ammonia. This protein metabolism takes place in the liver and thus, urea is produced by the liver. Further, urea is transferred to the kidney from the liver through the bloodstream and is excreted out of the body in the form of urine. Thus, any dysfunction of the kidney causes high or low amount of BUN in the blood.
Creatinine is a break-down product of creatine phosphate in muscle metabolism and is produced from creatine. It is basically a chemical waste that is transported to the kidneys through the bloodstream. The kidneys then filter this creatinine and flush out maximum amount of it through urine. Creatinine levels can be measured in urine as well as blood. The creatinine level in blood normally remains constant because the muscle mass is relatively constant. Thus, we can say that the normal functioning of the kidneys leads to normal levels of creatinine in the blood. But when the kidneys do not function properly, the amount of creatinine in the blood automatically increases. Now, let us take a look at what are the normal BUN creatinine ratios and what are the causes of low and high BUN creatinine ratios.
BUN-to-Creatinine Ratio
From the above discussion, it is clear that both BUN and creatinine are important elements of blood that help to detect problems in kidney functioning. The normal BUN-to-creatinine ratio is between 10:1 to 20:1 and the BUN creatinine ratio in children less than 12 months, is up to 30:1. When there are renal problems, the BUN-to-creatinine ratio increases due to increase in the amount of BUN and creatinine in the blood. But some health conditions can cause only the BUN or only creatinine to increase or decrease.
For example, a high protein diet causes the BUN level in the blood to increase, without affecting the levels of creatinine. On the other hand, there are medical conditions, such as liver cirrhosis and heart failure, that elevate the levels of BUN and creatinine, even when the kidneys are functioning properly. Given below is a list of various causes that can lead to high and low creatinine levels.
Causes of High BUN Creatinine Ratio
  • Kidney failure
  • Severe dehydration
  • Urinary tract blockage
  • Gastrointestinal tract bleeding
  • High protein diet
  • Steroid medications
Causes of Low BUN Creatinine Ratio
  • Low protein diet
  • Muscle injury (rhabdomyolysis)
  • Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)
  • Pregnancy
  • Cirrhosis
There are various factors that affect the BUN creatinine ratio. In older people, due to decreased muscle mass, the creatinine levels are low, which leads to a high BUN-to-creatinine ratio. Creatinine levels are also low in pregnant women, and hence can cause an elevated BUN-to-creatinine ratio. Dehydration causes BUN levels to increase without affecting the creatinine ratio. Thus, before going for a blood test to find out the BUN creatinine ratio, all these factors should be considered.