Before starting dialysis, the doctor assesses the kidney function. Blood urea level and creatinine are two important factors that help in knowing the kidney function and the degree and severity of kidney disease. It is generally noticed that both of these- the blood creatinine and blood urea levels increase and decrease proportionally in a given patient. However, there are some exceptions also.
Through this article, I will discuss common questions and their answers regarding BUN.
Blood urea normal range in India
The normal range of blood urea level in India can be interpreted from the table below:
| Blood urea level | Blood urea nitrogen(BUN) | |
| Adult man | 8-24mg/dl | 16-23mg/dl |
| Adult woman | 6-21mg/dl | 14-17mg/dl |
The value has a wide range because it depends on many external factors. Blood urea level can change with age, health status, dietary intake, medicine intake, etc. of the patient.
Blood urea nitrogen vs urea
Urea is a metabolic waste product. When proteins in the body are broken down, ammonia is released. Since ammonia is very toxic if present in blood, our liver converts ammonia into urea. This urea is then sent to kidneys.
One of the constituents of urea is nitrogen. The BUN test measures this nitrogen from the blood. The amount of urea is approximately double the nitrogen estimated from the BUN test. So, for example, if the BUN test value of a patient is 12mg/dl, it means that urea level is around 24.5mg/dl.
The end goal of dialysis is a healthy and, if possible, a happy patient. .
Urea and creatinine tests
Urea and creatinine levels are measured to assess the filtration rate of the kidney. This filtration rate, popularly known as Glomerular Filtration Rate, varies with age, sex, health status, progression of kidney disease etc. The relationship of creatinine and urea blood levels with GFR is very complex.
In earlier stages of kidney disease, the test results of BUN and creatinine levels may not show much variation while the GFR continuously falls to about 50% of normal value. However, in chronic kidney diseases and in patients who are in long term dialysis, these two tests can together reflect the status of GFR accurately.
Out of the two, creatinine tests are generally more reliable. It is so because the level of blood urea partly depends on external factors like the diet and medications of the patient. On the other hand, blood creatinine levels are mostly dependent on the kidney function.
Then why do we still measure blood urea? Urea and creatinine are linked to each other in a 10:1-20:1 ratio. So the increase or decrease in this ratio can help in pointing out the exact reason for kidney failure. Together, these tests are great indicators of GFR.
Now, coming to the most important question:
What levels of BUN indicates kidney failure?
As already mentioned, normal BUN levels vary between 5-20mg/dl. The level in an individual will depend on dietary intake, hydration levels, liver functions, kidney function, medications etc..
The wide range makes it difficult to point at one specific value that would qualify for kidney failure. To put this into context, for a person who consumes a protein-rich diet, the BUN value of 20mg/dl would be considered normal, However, the same value may be very high for a pregnant woman since her normal levels are between 5-7mg/dl.
This is why nephrologists often combine BUN with creatinine to estimate the progression of kidney failure.
Any level that is grossly above normal (for example 50 mg/dl) indicates that significant kidney disease is present. Higher the level, more severe the underlying disease.
At what levels of urea, dialysis is required?
The exact level of urea at which dialysis should be started is not fixed. It varies from patient to patient. On the other hand, very high levels of urea (more than 200 mg/dl) are generally accompanied by signs and symptoms which need dialysis.
The levels of blood urea depend on many factors. So, a proper assessment of urea with blood creatinine levels, potassium levels, medical history, haemoglobin, symptoms etc. should be made. It will help in judging the stage and severity of kidney failure.
The decision to initiate dialysis is not based on blood urea levels alone. All the above factors are taken into consideration before suggesting dialysis for a patient.
Blood urea level after dialysis
In a patient undergoing dialysis, the blood urea levels fall down by 60-70% after a session. Since blood urea depends on protein consumption among other things, it is expected to rise again.
So, with every dialysis, the level comes down and then, again increases in a few days.
That is why most patients with kidney failure need regular thrice a week dialysis.
Conclusion
Blood urea level test or BUN test is an indicator of Nitrogen in blood. The level of BUN can widely vary based on the patient’s unique history. The correct time to start dialysis can be decided by a nephrologist based on many factors.
I hope this article was helpful to you.
