Home Biomarkers Blood Urea

Blood Urea

Kidney Biomarker

Sample Needed

Collection Type: Blood

Body System

Related System: Kidney

Overview

Blood urea (often reported as BUN blood urea nitrogen or as serum urea) is a waste product formed in the liver from breakdown of proteins and amino acids; it carries excess nitrogen to the urine. The blood urea test measures how much urea is circulating and is used to assess kidney excretory function and protein metabolic state. Elevated values suggest reduced renal clearance (acute or chronic kidney disease), dehydration, high protein intake or catabolism, or gastrointestinal bleeding. Low values can indicate impaired liver urea synthesis, malnutrition, or fluid overload. Symptoms prompting the test include reduced urine output, swelling, persistent fatigue, nausea/vomiting, confusion, or unexplained breathlessness. Normal values vary slightly with age (infants and elderly differ), pregnancy (usually lower), and with dietary protein intake; gender differences are minimal.

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Test Preparation

No special preparation is required

Why Do I Need This Test

Profile: Kidney - Symptoms: decreased urine, oedema, unexplained fatigue, nausea, confusion, shortness of breath.
Diagnoses/monitoring: evaluates kidney function, monitors known renal disease, assesses hydration status, monitors treatment effects.
Reasons for abnormal levels: reduced renal clearance, dehydration, high protein intake, liver dysfunction, bleeding into the gut.
Biological meaning: high urea = accumulation of nitrogenous waste from reduced excretion or increased production; low urea = decreased production or dilution.
Lifestyle/factors: high-protein diet, fasting, heavy exercise, alcohol, dehydration, certain medications.
Family history: hereditary renal disease or familial liver disorders may indicate need for testing.

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Understanding Test Results

Values within 7–20 mg/dL are considered normal.
Mild elevation (≈21–50 mg/dL) commonly indicates prerenal causes such as dehydration, heart failure, high protein intake or catabolic states; it can also reflect early renal impairment.
Marked elevation (>50 mg/dL) suggests significant renal dysfunction, urinary obstruction, major gastrointestinal bleeding, or severe catabolism; values >100 mg/dL are usually seen in severe renal failure or massive bleed and require urgent evaluation.
Low values (<7 mg/dL) may result from advanced liver disease (reduced urea synthesis), malnutrition, overhydration, or pregnancy and are not generally harmful by themselves but signal underlying pathology.
Interpreting urea together with serum creatinine and the BUN:creatinine ratio (a high ratio, often >20:1, favors prerenal causes) improves diagnostic accuracy.
Clinical context, hydration status, diet and medications must be considered.

Normal Range

7-20 mg/dL OR 2.5-7.1 mmol/L

FAQs

Q: What happens if your blood urea is high?

A: High blood urea (elevated BUN) commonly signals reduced kidney clearance, dehydration, high protein intake, heart failure, severe infection, or urinary obstruction. It may coincide with fatigue, swelling, nausea, confusion or no symptoms at all. It indicates impaired waste removal and warrants checking creatinine, urine tests and fluid status. Treatment targets the underlying cause rehydration, adjusting medications, treating infections or relieving obstruction under medical supervision.

Q: What are normal blood urea levels?

A: Normal blood urea (serum urea) for adults is about 2.5–7.1 mmol/L (7–20 mg/dL). Some labs report blood urea nitrogen (BUN) with a normal range roughly 7–20 mg/dL; the urea values above are equivalent. Slight variations occur by lab, age, hydration and muscle mass; persistently high levels suggest dehydration or impaired kidney function and merit medical review.

Q: What if blood urea is low?

A: Low blood urea (low BUN) often reflects overhydration, low dietary protein or malnutrition, or reduced hepatic urea production (severe liver disease). It can also occur in pregnancy or certain hormonal states. Mild isolated reductions are usually not harmful, but persistent or marked low values warrant review of hydration, nutrition and liver function. Discuss abnormal results with your clinician for targeted testing and management.

Q: Is high urea good or bad?

A: High blood urea is generally not good it usually signals reduced kidney clearance, dehydration, high protein intake, internal bleeding, or effects of certain drugs. Mild rises may be reversible with rehydration or stopping offending medicines, but persistent elevation often indicates kidney disease. Medical evaluation (creatinine/eGFR) is needed to find the cause and guide treatment.

Q: Can drinking water reduce blood urea?

A: Yes drinking adequate water can lower blood urea when dehydration is the main cause. Good hydration dilutes plasma and helps the kidneys excrete urea, often reducing lab values. If high urea is due to chronic kidney disease, high protein intake, or other medical problems, fluids alone may be insufficient. Persistent elevation should be assessed and managed by a healthcare professional.

Q: What diseases cause high urea?

A: High urea (elevated blood urea nitrogen) is caused by impaired kidney function—acute kidney injury or chronic kidney disease—plus reduced renal perfusion from dehydration, heart failure, or shock. Post-renal obstruction (kidney stones, enlarged prostate), increased protein breakdown (severe burns, trauma, corticosteroid use), gastrointestinal bleeding, and sepsis can also raise urea levels.