Blood urea nitrogen
Blood urea nitrogen (BUN) is a medical test that measures the amount of urea nitrogen found in blood.
The liver produces urea in the urea cycle as a waste product of the digestion of protein.
The adult blood should contain 6 to 20 mg/dL of urea nitrogen.
The BUN test is used to detect renal problems, but not considered as reliable as creatinine or BUN/creatinine ratio blood studies.
BUN elevations are caused by: high protein diet, decrease in glomerular filtration rate (GFR), decrease in blood volume, congestive heart failure, gastrointestinal hemorrhage,fever, rapid cell destruction from infections, athletic activity, excessive muscle breakdown, and increased catabolism.
Hypothyroidism can cause both decreased GFR and hypovolemia
BUN-to-creatinine ratio has been found to be lowered in hypothyroidism and raised in hyperthyroidism.
The causes of a decreased BUN are: severe liver disease, anabolic state, and syndrome of inappropriate antidiuretic hormone.
Ornithine transcarbamylase deficiency, is a genetic disorder inherited in an X-linked recessive pattern, associated
with hyperammonemia and high orotic acid levels.