Blood Urea Nitrogen (BUN)

Low blood urea nitrogen (BUN) often reflects overhydration, reduced liver urea production (liver disease), very low protein intake or malnutrition, pregnancy, or certain hormonal conditions (e.g., SIADH). It’s usually asymptomatic; clinical assessment focuses on hydration status, liver function tests, nutritional evaluation and medication review. Management treats the underlying cause—adjust fluids, improve protein intake, or address liver/hormonal disorders—and repeat testing.

A high blood urea nitrogen (BUN) indicates elevated urea in the blood, often reflecting reduced kidney clearance or increased protein breakdown. Common causes include dehydration, acute or chronic kidney injury, high-protein diet, gastrointestinal bleeding, or heart failure. It prompts assessment of kidney function (creatinine, BUN/creatinine ratio), fluid status, and underlying conditions; further tests and treating dehydration or kidney disease follow.

Typical BUN ranges by age: - Newborns: about 3–12 mg/dL - Infants and children: about 5–18 mg/dL - Adults: about 7–20 mg/dL - Older adults: may be slightly higher, up to ~25 mg/dL Reference ranges vary by laboratory; results should be interpreted with clinical context and other kidney function tests. If concerned, discuss with your clinician.

An urea test in pregnancy measures blood urea (blood urea nitrogen) to assess kidney function and protein metabolism. Pregnancy usually lowers urea because of increased filtration; elevated urea may signal dehydration, impaired renal function or complications such as severe pre-eclampsia. Results are interpreted with creatinine, electrolytes and clinical findings to monitor maternal kidney health, especially in those with preexisting renal disease.

Serum urea normal: about 2.5–7.8 mmol/L (BUN 7–20 mg/dL). Values below the lower limit (urea <2.5 mmol/L or BUN <7 mg/dL) are considered low; levels under roughly 1.7 mmol/L (BUN <5 mg/dL) are more concerning and may indicate severe liver disease, malnutrition, overhydration, or SIADH. Markedly low urea warrants clinical review and liver-function tests.

Yes. The liver converts ammonia to urea, so significant liver damage or failure can reduce urea synthesis and cause low blood urea (BUN) while ammonia rises, raising hepatic encephalopathy risk. Mild liver disease may not lower urea. Other causes of low urea include low dietary protein, malnutrition, pregnancy or fluid overload, so results need clinical correlation.