BUN (urea nitrogen)
What it measures, and what changes the number.
BUN, or blood urea nitrogen, measures the nitrogen contained in urea, a waste product the liver makes when it breaks down protein and the kidneys then filter out. It reflects the same molecule as a urea result, expressed as its nitrogen content, which is the convention in the United States and some other countries.
It is nearly always read with creatinine and eGFR as part of a kidney or basic metabolic panel, and some reports show a BUN to creatinine comparison. Electrolytes such as sodium and potassium are usually on the same panel.
The value is influenced by recent protein intake and hydration at the time of the draw. Because BUN and urea use different units, the two cannot be compared without conversion. Reports may label it UREA NITROGEN (BUN).
Often read alongside: Creatinine, eGFR (CKD-EPI), Urea, Sodium, Potassium