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Blood Urea Nitrogen

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Measurement of urea nitrogen in blood (or blood urea) along with creatinine are the most common tests to evaluate kidney function. In the United States, the measurement of urea nitrogen is more common, while in Europe and Greece the measurement of urea is more common. It is practically the same test. Blood urea nitrogen and blood urea are related according to the following mathematical relation: Blood Urea Nitrogen (mg/dL) = Blood Urea (mg/dL) / 2.1428

It is usually referred to as BUN (Blood Urea Nitrogen). Urea nitrogen is part of urea, a substance that is formed in the liver through the enzymatic process of protein catabolism. The urea is normally filtered freely through the renal glomeruli, with a small proportion being reabsorbed in the tubules and the remainder excreted in the urine. The pathological condition where there are elevated levels of urea nitrogen in the blood is called azotemia. However, urea nitrogen is a nonspecific test as to the cause, which can have either prerenal, renal, or post-renal origin.

In prerenal causes, factors that lead to inadequate renal circulation or conditions resulting from abnormally high protein levels in the blood can be grouped.

Renal causes are those associated with renal filtration and urea nitrogen excretion.

Post-renal causes are those associated with obstructive conditions of the lower urinary tract and which result in the diffusion of urine nitrogen back into the bloodstream.

Uremia is a term used to describe symptoms that occur at very high concentrations of urea in the blood and can occur at levels of urea nitrogen greater than 200 mg/dL (> 70 mmol/L). Also important are low levels of urea nitrogen in severe liver disease. A damaged liver that is unable to synthesize urea from protein catabolism results in an increase in blood ammonia (NH3) concentration, causing hepatic encephalopathy.

What Do Pathological Values Mean?
  • Increase: Addison's disease, allergic purpura, amyloidosis, analgesics abuse, blood transfusions, cachexia, heart failure, congenital kidney hypoplasia, dehydration, diabetes mellitus, diabetic ketoacidosis, diet (high protein), Fanconi syndrome, excessive hydration, gastrointestinal bleeding, glomerulonephritis, Goodpasture syndrome, gout, heavy metal poisoning, hemoglobinuria, infection, intestinal obstruction, multiple myeloma, myocardial infarction (acute), nephritis, nephropathy (hypercalcemic, hypokalemic), nephrosclerosis, pancreatitis, peritonitis, pneumonia, polyarteritis nodosa, polycystic disease, post-operative condition, protein intake (excessive), pyelonephritis, renal artery stenosis or thrombosis, kidney cortical necrosis, renal neoplasms, kidney tuberculosis, renal vein thrombosis, scleroderma, sepsis, shock, sickle cell anemia, hunger, anxiety, subacute bacterial endocarditis, suppuration, systemic lupus erythematosus, thyrotoxicosis, tumor necrosis, uremia, urinary tract obstruction. Medications: acetohexamide, acetone, antacids, aminophenol, ammonium salts, amphotericin B, anabolic steroids, androgens, antimony compounds, arginine, arsenic, ascorbic acid, asparaginase, bacitracin, calcium salts, capreomycin, captopril, carmustine, cephaloridine, chloral, chloramphenicol, chlorobutanol, sodium chlorothiazide, chlorthalidone, clonidine, colistimethate, dextran, dextrose, disopyramide, doxapram, ethacrylic acid, fluphenazine, fosinopril,  guanethidine, hydroxyurea, indomethacin, kanamycin, lithium carbonate, marijuana, meclofenamate sodium, mephenesin, mercury compounds, diuretics, methicillin, methoxyflurane, methsuximide, methyldopa, methylprednisolone sodium succinate, methysergide, metolazone, metoprolol tartrate, mithramycin, morphine, nalidixic acid, naproxen, neomycin, nitrofurantoin, paramethasone, polymyxin B, propranolol, salicylates, spectinomycin, streptodornase, streptokinase, sulfonylureas, tetracycline, thiazide diuretics, tolmetin, triamterenium, vancomycin.
  • Decrease: Acromegaly, alcohol abuse, amyloidosis, celiac disease, cirrhosis, diet (inadequate protein intake), fluid intake (excessive), dialysis, hepatitis, childhood, liver damage, malnutrition, kidney disease, increase in plasma volume, pregnancy. Medications: chloramphenicol, streptomycin, thymol.


Important Note

Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. The correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".

Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings, and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.

At Diagnostiki Athinon we answer any questions you may have about the test you perform in our laboratory and we contact your doctor to get the best possible medical care.


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