Normal Blood Urea Nitrogen (BUN) Values
Apr 08, 2021
Source: Cainiu Health
Dr. Ma Fujun
Introduction
Blood urea nitrogen (BUN) reference ranges vary with age:
- Newborns: 1.4–4.3 mmol/L
- Children: 1.8–6.4 mmol/L
- Adults: 2.5–6.4 mmol/L
- Elderly individuals: 2.9–7.5 mmol/L
Blood urea nitrogen (BUN) refers to the concentration of urea nitrogen in plasma—specifically, a non-protein nitrogenous compound that is filtered through the glomeruli and excreted from the body via urine. When renal function deteriorates and compensation fails, BUN levels rise. Thus, clinicians use BUN as an indicator to assess glomerular filtration function. So, what constitutes a normal BUN level? The following section provides clarification.
Normal BUN Values
Normal BUN values vary with age: in newborns, the reference range is typically 1.4–4.3 mmol/L; in children, it is 1.8–6.4 mmol/L; in adults, 2.5–6.4 mmol/L; and in elderly individuals, 2.9–7.5 mmol/L. Abnormal BUN levels often reflect impaired renal function; however, BUN alone is not a definitive diagnostic criterion. Additional auxiliary tests are required to confirm renal dysfunction. The test procedure parallels routine urinalysis: a clean, dry container should be used—preferably the disposable urine cup and tube provided by the hospital. Approximately 10 mL of urine should be collected and submitted to the designated laboratory window at the hospital for analysis using isotopic methods or microscopic examination. For optimal accuracy, fresh first-morning urine is recommended; if random sampling is performed, midstream urine is preferred.
Additional Information: Clinical Significance of BUN
1. Urea nitrogen is a metabolic end-product of protein catabolism, with over 90% excreted by the kidneys and the remainder eliminated via the gastrointestinal tract and skin. When renal pathology impairs normal excretory function, blood urea nitrogen concentrations increase. Consequently, serum BUN serves as an important marker of renal functional status.
2. Decreased BUN levels may occur in severe hepatic disorders, such as fulminant hepatitis with extensive hepatocellular necrosis. Elevated BUN levels may be observed in conditions including acute glomerulonephritis, advanced kidney disease, renal failure, chronic pyelonephritis, toxic nephritis, benign prostatic hyperplasia, urinary calculi, urethral stricture, bladder tumors, severe vomiting, pyloric obstruction, intestinal obstruction, and prolonged diarrhea.
The above outlines normal BUN reference ranges. We hope this information proves helpful to you.
