Ares, Bea ClaireGayam, Glydenne Glaire

Blood Urea Nitrogen (BUN)

• Urea Nitrogen – measurement of the amount of urea nitrogen in the blood

• Conversion Factor: 0.357• Urea CO (NH2)2 ; MW: 60 Da• Major end product of protein (dietary) and amino

acid catabolism • Synthesized by liver from ammonia. Excreted by

kidneys.• 1st metabolite to increase in kidney disease• BUN x 2.14 = Urea; Urea x 0.467 = BUN

Reference Values

Normal• Adults: 6–20 mg/dL or 2.1–7.1 mmol/L• Elderly patients ( 60 years): 8–23 mg/dL or

2.9–8.2 mmol/L• Children: 5–18 mg/dL or 1.8–6.4 mmol/L

• Normal BUN:Creat ratio = 10:1 – 20:1

Procedure: Pre-analytical Considerations

• Explain test purpose and blood drawing procedure to the patient

• Patient is taking any medication• Specimen– Serum or Plasma; Urine (24hr)– Should be analyzed w/in few hrs after collection or

preserved by refrigeration (4°-8°C up to 72hrs, ph<4)• Anticoagulants containing fluoride (gray-top

evacuated tubes) or citrate should be avoided

Procedure: Pre-analytical Considerations

• Fasting sample – not required• Non-hemolyzed sample• No interferences from biliribun & lipemia• Thiosemicarbazide and Ferric ions are added

Analytical Methods

Chemical Method (Direct Method)• Diacetyl Monoxime Method• Urea + DAM → Yellow Diazine Derivative

Analytical Methods

Enzymatic Method (Indirect Method)a. Hydrolysis of Urea by Urease• Urea + Urease → NH3 + CO2 • Ammonia produced treated w/ Berthelot Reagents• NH3 & CO2 : measured by various methods to calculate

urea in original sample. Measurement of Ammonia is most often used.

Isotope Dilution Mass Spectrometry (IDMS) – reference method

Clinical Implications

Increased BUN levels (azotemia)• Impaired renal function caused by

1. Congestive heart failure2. Salt and water depletion3. Shock4. Stress5. Acute MI

Clinical Implications

Increased BUN levels (azotemia)• Chronic renal disease such as

glomerulonephritis and pyelonephritis• Urinary tract obstruction• Hemorrhage into GI tract• Diabetes mellitus with ketoacidosis• Excessive protein intake or protein catabolism

as occurs in burns or cancer• Anabolic steroid use

Clinical Implications

Decreased BUN levels• Liver failure (severe liver disease), such as that

resulting from hepatitis, drugs, or poisoning• Acromegaly• Impaired absorption (celiac disease)• Nephrotic syndrome (occasional)• Syndrome of inappropriate antidiuretic

hormone (SIADH)

Interfering Factors1. Combination of a low-protein and high-carbohydrate diet

can cause a decreased BUN level.2. BUN is normally lower in children and women because

they have less muscle mass than adult men.3. Decreased BUN values normally occur in late pregnancy

because of increased plasma volume (physiologic hydremia).

4. Older persons may have an increased BUN when their kidneys are not able to concentrate urine adequately.

5. IV feedings only may result in overhydration and decreased BUN levels.

6. Many drugs may cause increased or decreased BUN levels.

END“Give up trying to do everything myself and depended on Him even for the smallest of

things.”