Blood urea nitrogen (BUN)

A BUN, or blood urea nitrogen test, can provide important information about your kidney function. The main job of your kidneys is to remove waste and extra fluid from your body. If you have kidney disease, this waste material can build up in your blood. Over time, this may lead to serious health problems, including high blood pressure, anaemia, and heart disease.

The BUN test measures the amount of urea nitrogen in your blood. Urea nitrogen is a waste product that your kidneys remove from your blood. Higher than normal BUN levels may be a sign that your kidneys aren't working well.

People with early kidney disease may not have any symptoms. A BUN test can help uncover kidney problems at an early stage when treatment can be more effective.

However, blood urea nitrogen (BUN) and creatinine will not be raised above the normal range until 60% of total kidney function is lost. Hence, the more accurate Glomerular filtration rate or its approximation of the creatinine clearance is measured whenever renal disease is suspected or careful dosing of nephrotoxic drugs is required.

Another prognostic marker for kidney disease is an elevated level of protein in the urine. The most sensitive marker of proteinuria is elevated urine albumin. Persistent presence of more than 30 mg albumin per gram creatinine in the urine is diagnostic of chronic kidney disease (microalbuminuria is a level of 30–299 mg/L urine or 30-299 mg/24 hrs; a concentration of albumin in the urine that is not detected by usual urine dipstick methods).

Higher than normal BUN levels can also be caused by dehydration (too little fluid in your body), burns, certain medicines, a high protein diet, or other factors, including your age. BUN levels normally increase as you get older.

What does high blood urea nitrogen mean?

High BUN levels may suggest that your kidneys aren’t working as they should. However, even if your kidneys are working properly, you may have elevated BUN levels from the following:

High-protein diet.

Dehydration.

Aging (infants and children have lower BUN levels).

Certain medications, including carbamazepine, methotrexate and tetracycline.

Burns.

Blockage in your urinary system that prevents you from peeing.

Stress.

Heart attack.

Gastrointestinal (GI) bleeding.

What does low blood urea nitrogen mean?

Low BUN levels aren’t common. However, you may have low BUN levels from the following:

Low-protein diet.

Small body type.

Overhydration (too much water in your body).

Liver disease.

1.                    https://medlineplus.gov/lab-tests/bun-blood-urea-nitrogen/#:~:text=Urea%20nitrogen%20is%20a%20waste,treatment%20can%20be%20more%20effective.

2.                     https://my.clevelandclinic.org/health/diagnostics/17684-blood-urea-nitrogen-bun-test

3.                     https://www.ncbi.nlm.nih.gov/books/NBK305/

4. Bauer JH, Brooks CS, Burch RN. Renal function studies in man with advanced renal insufficiency. Am J Kidney Dis. 1982;11:30–35. [PubMed]
5. Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16:31–41. [PubMed]
6. Doolan PD, Alpen EL, Theil GB. A clinical appraisal of the plasma concentration and endogenous clearance of creatinine. Am J Med. 1962;32:65–79. [PubMed]
7. Dosseter JB. Creatininemia versus uremia. Ann Intern Med. 1966;65:1287–99. [PubMed]
8. Kassirer JP. Clinical evaluation of kidney function: glomerular function. N Engl J Med. 1971;285:355–89. [PubMed]
9. Mitch WE, Collier WU, Walser M. Creatinine metabolism in chronic renal failure. Clin Sci. 1980;58:327–35. [PubMed]
10. Narayanan S, Appleton HD. Creatinine: a review. Clin Chem. 1980;26:1119–26. [PubMed]
11. Raforth RJ, Onstad GR. Urea synthesis after oral protein ingestion in man. J Clin Invest. 1975;56:1170–74. [PMC free article] [PubMed]