BUN (blood urea nitrogen) is a measurement of the nitrogen part of urea, and is therefore an indirect measurement of the urea in the bloodstream.
A blood urea Nitrogen (BUN) test is used to determine how well your kidneys are working. It does this by measuring the amount of urea nitrogen in the blood. Urea is a waste product that’s created in the liver when the body breaks down proteins. Normally, the kidneys filter out this waste, and urinating removes it from the body.
|Also Known as||BUN, Urea Nitrogen, Blood Urea Notrogen, Serum BUN, Urea Nitrogen Test|
|Test Purpose||BUN is a measurement of the Nitrogen in the bloodstream.|
|Test Preparations||No Special Preparation Required.|
|Test Components||BUN, Blood Urea|
|Specimen||2 ML (0.5 ML Min.) Serum From 1 SST. Ship Refrigerated Or Frozen.|
|Stability Room||2 Hours|
|Stability Refrigerated||1 Week|
|Stability Frozen||2 Weeks|
|Download Report||Download Report|
BUN levels tend to increase when the kidneys or liver are damaged. Having too much urea nitrogen in the blood can be a sign of kidney or liver problems.
Why Get Tested:
- To assess the renal function.
- As a routine test in the patient with dialysis.
- To assess liver function.
- This may be part of the routine test.
- In patients:
- Has nonspecific symptoms.
- During the hospital stay.
- Prior to some drug therapy.
- Acutely ill patient admitted in an emergency.
When to get Tested:
- As part of a routine comprehensive or basic metabolic panel (CMP or BMP) during a health exam.
- When you have signs and symptoms that may be due to kidney disease or you have a condition that may cause or be worsened by kidney dysfunction.
- At regular intervals when you are being treated for kidney disease or damage.
- This is done on the serum of the patient.
- No special preparation is needed.
Precautions for Sample:
- If there is Fluoride that will inhibit Urease reaction.
- Avoid hemolysis.
- Protein intake will affect BUN. Low protein diet will give low BUN.
- High protein diet or nasogastric tubing will increase BUN.
- Keep in mind muscle mass which is more in males than females and children.
- Overhydrated patient will dilute the BUN and gives a lower value.
- The dehydrated patient will concentrate BUN and gives high value.
- GI bleeding can cause an increase in BUN level.
- Advanced pregnancy may increase the BUN level.
- Drugs increasing the BUN level are cephalosporin, indomethacin, gentamicin, polymyxin B, rifampicin, bacitracin, neomycin, tetracycline, thiazide diuretics, and aspirin.
- There are drugs which decrease the BUN level are streptomycin and chloramphenicol.
- Urea = 20 to 40 mg/dl
- Blood urea nitrogen (BUN) = 10 to 20 mg /dl
Increased Urea (BUN) Azotemia seen in:
A. Impaired renal function:
- congestive heart failure and Myocardial infarction (CHF).
- Salt and water depletion
- Acute MI
- Hemorrhage into GI tract
- excessive protein catabolism.
B. Chronic renal diseases:
- Glomerulonephritis (GN).
- Pyelonephritis (PN).
- Acute tubular necrosis.
- Renal failure.
- Diabetes mellitus with ketoacidosis.
- Anabolic steroids use.
- Nephrotoxic drugs.
C. Urinary tract obstruction:
- Ureteral obstruction from stones, tumors, or congenital abnormality.
- Bladder outlet obstruction from prostatic hypertrophy, cancer.
- Bladder / urethral congenital abnormality.
Decreased Urea (BUN) seen in:
- Liver failure.
- Malnutrition, and low protein diet.
- Impaired absorption of Celiac disease.
- Syndrome of inappropriate antidiuretic hormone secretion.
- Nephrotic syndrome.
Effect of drugs and other condition on a BUN:
- Some of the drugs may cause a decrease in BUN like Dextrose infusion, Phenothiazine, and Thymol.
- Increased BUN level may be seen in late pregnancy and infancy because of increased use of proteins.
- The normal BUN/creatinine ratio is around 10:1.
- BUN/creatinine ratio in the normal range, in the case of raised BUN and creatinine. This will suggest intrarenal disease:
- Tubulointerstitial nephritis.
- When the BUN / Creatinine ratio is raised will suggest:
- Prerenal azotemia.
- Postrenal azotemia.
- These conditions may be seen in hypovolemia or hypotension.
- BUN/creatinine ratio decreased is very rare and this may be seen in:
- Protein deficiency in the diet.
- In severe liver disease.
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