The blood urea test is used mainly to test the renal (kidney) function. In kidney diseases, there is an increase in the blood urea level due to reduced excretion by the kidneys.

In protein metabolism, urea is formed in the liver as the end product. Protein is broken down to amino acids during digestion. Amino acids contain nitrogen that is split off as the ammonium ion (NH4). The ammonium ion combines with other small molecules to produce urea. The urea is passed into the blood and excreted by the kidneys in the urine. Blood urea levels go up in most kidney diseases as urea excretion is affected. It may also be high in patients with liver disease or dehydration. A large number of drugs increase blood urea level by competing with it for excretion by the kidneys.

Blood is drawn from a vein by venepuncture, usually from the inside of the elbow. No special preparation is required for the test.

7 to 20 mg/dl.

More-than-normal values could be due to:
 

• Kidney diseases like glomerulonephritis, pyelonephritis, and acute tubular necrosis
• Renal (kidney) failure
• Too much protein breakdown like in starvation
• Very high protein intake
• Congestive heart failure
• Heart Attack
• Bleeding in the gut
• Decrease in the blood volume like in burns, dehydration or shock
• Obstruction in the urinary tract due to a tumour, stones, or prostatic hypertrophy
• Drugs used in gout, infections, epilepsy, blood pressure, pain relief, etc may raise blood urea. These include allopurinol, aminoglycosides, cephalosporins, chloral hydrate, furosemide, indomethacin, methotrexate, methyldopa, drugs toxic for the kidneys (like high doses of aspirin, amphotericin B, carbamazepine, colistin, penicillamine, polymyxin B, probenecid, vancomycin), propranolol, rifampin, spironolactone, tetracyclines, thiazide diuretics, and triamterene.

Lower-than-normal levels may be due to:

Low protein diet, malnutrition or too much fluid intake

Liver failure

Drugs to treat some infections like chloramphenicol and streptomycin