Q: Context: 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. Normal human adult blood should contain between 6 and 20 mg of urea nitrogen per 100 ml (6 -- 20 mg / dL) of blood. Individual laboratories will have different reference ranges as the assay used will vary between laboratories.

Question: what is the normal range for urea nitrogen?
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Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
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To answer this question, we should know that: Normal human adult blood should contain between 6 and 20 mg of urea nitrogen per 100 ml (6 -- 20 mg / dL) of blood. So the answer is between 6 and 20 mg of urea nitrogen per 100 ml ( 6 -- 20 mg / dL ) of blood.