Lab practical report on blood urea-Nitrogen (BUN) test

1. KENYATTA UNIVERSITY
SCHOOL OF MEDICINE.
DEPARTMENT OF MEDICAL BIOCHEMESTRY
NAME: LANDO ELVIS OTIENO
REG NO: P29S/16344/2015.
COURSE: MBCHB
LECTURER: Prof NJAGI/Mr KIM
HANDING DATE: /3/2016
SUBJECT: PRACTICAL REPPORT ON ESTIMATION OF BUN.
ELVIS
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2. BACKGROWND
The determination of serum blood urea nitrogen currently is the most widely used screening test for the
evaluation of kidney function. The test is frequently requested along with the serum creatinine test since
simultaneous determination of these 2 compounds appears to aid in the differential diagnosis of prerenal,
renal and postrenal hyperuremia.
Principle
Urea is the principle waste product of protein catabolism. It is synthesized in the liver from ammonia
which is produced as a result of the deamination of amino acids. Normally, urea nitrogen in the blood
comprises only about 45% of the non-protein nitrogen. The diacetyl monoxime methodology for BUN
determination is direct and measures a chromogen formed from the condensation of urea with diacetyl
This condensation methodology does not suffer from ammonia interference and utilizes less caustic
reagents than other methods. Diacetyl monoxime is hydrolyzed under acidic conditions to produce
diacetyl which then condenses with urea to form a pink chromogen that is measured at 520 nm.
Thiosemicarbazide and ferric ions are employed to enhance the color development.
Clinical Significance
While a high protein diet, administration of cortisol-like steroids and stressfulsituations can increase the
concentration of BUN, the test is generally used to detect prerenal(cardiac decompensation, water
depletion due to decreased intake and excessive loss, increased protein catabolism, and high protein diet),
renal glomerulonephritis, chronic nephritis, polycystic kidney disease, nephrosclerosis, and tubular
necrosis), and post-renal malfunction (eg, all types of obstruction of the urinary tract, such as stones,
enlarged prostate gland, tumors). increases in BUN are encountered with acute and chronic nephritis,
intestinal and urinary obstruction, metallic poisoning, pneumonia, uremia, Addison's disease, peritonitis,
surgical shock and cardiac failure. The BUN concentration is low in late pregnancy when the fetus is
growing rapidly and utilizing material amino acids, in starvation, and in patients whose diet is grossly
deficient in protein. decreased in BUN are also noted in nephrosis, acute liver destruction, and
amyloidosis
Materials Required
1. Spectrophotometer or suitable instrument calibrated to read absorbance at 520 nm.
2. Test tubes and Cuvets
3. Pipettes: 0.02 mL (20:L), 1.5 ml, & 3 ml
4. Timer or stopwatch.
5. Waterbath or heatblock capable of maintaining 100°C.

3. Procedure
1. Label three
(3) or more test tubes or cuvettes Blank, Standard, Test 1, Test 2, etc.
2. To each, add 1.5 mL BUN Color Reagent.
3. To Blank, add 20 :L water. To Standard(s) add 20 :L Urea Nitrogen Standard Solution. To Test add 20
:L serum or plasma
Mix contents by gently swirling.
4. Add 3.0 mL BUN Acid Reagent into all tubes, mix well.
5. Incubate for 10 minutes at 100°C in a heat block or 8 minutes in a boiling water bath.
6. Remove all tubes and cool to room temperature using cold tap water.
7. Mix all tubes prior to reading the absorbance.
8. Set the wavelength of the spectrophotometer at 520 nm. Zero with the Reagent Blank.
9. Read and record the absorbance( for the standard and test exactly after 30seconds and exactly
60seconds later
10. calculate change in absorbance for both standard and test.
Observations and calculations
sample Standard absorbance Test absorbance
At 30 seconds(A1) 0.481 0.523
At 60 seconds(A2) 0.485 0.565
Change in absorbance for standard= A2S – A1S
=0.485 – 0.481
Change in absorbance for test sample= A2T – A1T
=0.565-0.523
Urea in Mg/dl= (A2T – A1T) / (A2S – A1S)
=(0.565-0.523) / (0.485 – 0.481)
=10.5mg/dl

4. Urea in Mmol/L= 10.5 x 0.1665(constant)
=1.7483Mmol/L
Reference Values
Males
1-17 years:7-20 mg/dL
> or =18 years: 8-24 mg/dL
Reference values have not been established for patients who are <12 months of age.
Females
1-17 years:7-20 mg/dL
> or =18 years: 6-21 mg/dL
Reference values have not been established for patients who are <12 months of age.
Therefore the urea concentration for the this test is within standardized normal range.
Interpretation and conclusion
Serum blood urea nitrogen (BUN) determinations are considerably less sensitive than BUN clearance
(and creatinine clearance) tests,and levels may not be abnormal until the BUN clearance has diminished
to <50%. Clinicians frequently calculate a convenient relationship, the urea nitrogen/creatinine ratio:
serum bun in mg/dL/serum creatinine in mg/dL. For a normal individual on a normal diet, the reference
interval for the ratio ranges between 12 and 20, with most individuals being between 12 and 16.
Significantly lower ratios denote acute tubular necrosis, low protein intake, starvation or severe liver
disease. High ratios with normal creatinine levels may be noted with catabolic states of tissue breakdown,
prerenal azotemia, high protein intake, etc. High ratios associated with high creatinine concentrations may
denote either postrenal obstruction or prerenal azotemia superimposed on renal disease. Because of the
variability of both the BUN and creatinine assays,the ratio is only a rough guide to the nature of the
underlying abnormality. Its magnitude is not tightly regulated in health or disease and should not be
considered an exact quantity.

5. REFFERENCES
Tietz Textbook of Clinical Chemistry. Fourth edition. Edited by CA Burtis, ER Ashwood, DE Bruns. WB
Tietz, N.W.,ed. Clinical Guide to Laboratory Tests,3rd Ed. Philadelphia; W.B. Saunders: 1995.
National Committee for Clinical Laboratory Standards, How to Define, Determine, and Utilize Reference
Intervals in the Clinical Laboratory, Approved Guideline. Villanova, PA; NCCLS Publication C28-A:
1995.
Tietz, N.W.,ed. Fundamentals of Clinical Chemistry, 3rd Ed. Philadelphia; W.B. Saunders: 1987.
Saunders Company, Philadelphia, 2006;24:801-803