What causes an increase in BUN levels?

An increase in BUN (Blood Urea Nitrogen) levels is commonly associated with inadequate excretion at the kidneys. BUN is a waste product formed from the breakdown of protein in the liver, and it is normally excreted from the body through the kidneys. When kidney function is compromised—due to conditions such as acute or chronic kidney disease, dehydration, or obstruction of urinary flow—there is a reduction in the kidneys' ability to filter and eliminate urea from the bloodstream. This results in elevated BUN levels.

While excessive protein intake can also lead to increased BUN due to the higher amount of urea produced from protein metabolism, the direct cause of significantly elevated BUN in many clinical scenarios is often linked to renal function impairment. Inadequate kidney excretion overwhelms the body's ability to remove BUN, leading to its accumulation in the blood.

High fluid intake typically helps dilute blood components and can actually lower BUN levels, while increased muscle mass leads to higher protein metabolism but is less common as a primary cause of clinically significant BUN elevations. Therefore, the effect of kidney function is often the most critical factor in understanding BUN level changes.