Blood Urea Nitrogen

BUN stands for blood urea nitrogen. It measures the amount of nitrogen in your blood that comes from urea, a waste product your liver makes when it breaks down protein and your kidneys then clear. In medical terms it's a rough indicator of kidney function and hydration, though it's affected by diet and other factors, so it's usually read alongside creatinine and eGFR rather than on its own.

Most labs use a normal range of about 7 to 20 mg/dL for adults, though the exact reference range varies slightly by lab and can run a little higher with age. Values above the range often reflect dehydration, a high-protein diet, or reduced kidney function, while low values are usually benign. Read your specific number against the reference range printed on your own report.

A BUN of 14 is squarely in the normal range and nothing to worry about. A BUN of 20 sits right at the top of the typical range, and 24 is mildly above it — commonly seen with dehydration or a high-protein diet rather than kidney disease. A modestly elevated BUN with a normal creatinine and eGFR is usually not concerning, but your physician should interpret it in context.

A low BUN of around 3 mg/dL is generally not a health concern. It can occur with a low-protein diet, overhydration, or pregnancy, and sometimes with significant liver disease since the liver makes urea. On its own a low BUN in an otherwise healthy person rarely means anything worrisome, but mention it to your doctor if it's persistent or paired with other abnormal results.

Urea is the end product of protein breakdown, so eating a lot of protein — common among lifters and men on TRT — naturally produces more urea and pushes BUN toward or slightly past the top of the range without indicating kidney trouble. Dehydration compounds this by concentrating the blood. If your BUN is high but creatinine and eGFR are normal, diet and hydration are the usual explanation; hydrate well before a fasted draw and discuss any persistent elevation with your physician.

Compare your value to the reference range on the report (typically about 7 to 20 mg/dL) and look at it together with creatinine and eGFR, since those distinguish true kidney issues from diet and hydration effects. A number a point or two outside the range is rarely meaningful by itself. Trends across several tests are more informative than any single reading, and your doctor is the right person to interpret the full panel.