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Urea Nitrogen (BUN)
Intended Use
STANDARD (25 MG/DL) For in vitro diagnostic use in the quantitative colorimetric determination of A solution containing urea equivalent to 25 mg/dl with preservative. Avoid urea nitrogen in serum. contamination. Store at 2-8°C. Exercise the normal precautions required for the handling of al laboratory reagents. Pipetting by mouth is not recommended. Clinical Significance1
Urea, an end product of protein metabolism, is excreted by the kidney. Reagent Deterioration
Blood urea nitrogen (BUN) varies directly with protein intake and inversely with the rate of excretion of urea. Appearance of turbidity, visible mold growth, discoloration, or crystal formation that BUN levels are elevated under the following conditions: wil not readily dissolve 1. Renal insufficiency: acute and chronic nephritis, acute renal failure (tubular necrosis), urinary tract obstruction. Instrument Requirements
2. Increased nitrogen metabolism associated with diminished renal blood Any instrument capable of reading absorbance accurately with a sensitivity of flow or impaired renal function: dehydration from any cause, 0.005 absorbance at 630 nm may be used. The bandwidth should be less than 10 gastrointestinal bleeding, with a combination of increased protein nm, stray light of 0.5% or less, and the wavelength accuracy within 5 nm. absorption from digestion of blood, plus decreased renal blood flow. 3. Decreased renal blood flow: shock, adrenal insufficiency, occasional y Specimen3
congestive heart failure. Serum is recommended for the assay. Plasma may also be used, provided that 4. Many of the antibiotics that impair renal function; guanethidine, the anticoagulant used contains neither ammonium nor fluoride salts. Sodium, methyldopa, indomethacin, isoniazid, propranolol, and potent diuretics potassium, or lithium salts or heparin, EDTA, or oxalate are satisfactory (decreased blood volume and renal blood flow). BUN levels are decreased under the fol owing conditions: Urea in serum is stable up to 24 hours at room temperature, for at least several 1. Hepatic failure days at 4-6°C, and for at least 2-3 months when frozen. 2. Nephrosis not complicated by renal insufficiency 3. Cachexia (general poor health with weakness and malnutrition). Materials Provided
Enzyme reagent, color reagent, base reagent, standard (25mg/dl) Test History and Principle2
The Berthelot reaction, in which ammonia reacts with hypochlorite, phenol, a Materials Required but not Provided
catalyst, and alkali to produce a stable blue complex (indophenol) has been 1. Accurate pipetting devices known for over 100 years but only relatively recently used in a method for serum urea. The use of sodium nitroferricyanide was introduced in 1962 and the substitution of salicylate for phenol was introduced in 1967. 4. Spectrophotometer This procedure is based upon a modified Berthelot reaction wherein urease 5. 37°C heating bath hydrolyzes urea to ammonia and carbamic acid. Carbamic acid spontaneously decomposes into ammonia and carbon dioxide. Ammonia reacts with salicylate, nitroferricyanide and an alkaline solution of Procedure
hypochlorite to yield a blue-green chromophore which is measured photometrical y and is proportional to the amount of urea in the sample. 1. Transfer 0.5 ml of COLOR RGT to vials labeled: UNKNOWN, CONTROL, STANDARD, BLANK. Reagents
2. Add 0.010 ml (10ul) of sample to its corresponding vial. 3. Add 0.5 ml of ENZYME RGT to al vials, mix gently, and incubate at 37°C for The fol owing reagents should be stored at 2-8°C. and can be used until the five minutes. (Alternative: React for 10 minutes at room temperature 2- expiration date indicated on the individual bottle: 4. Add 2.0 ml of BASE RGT, mix and incubate at 37°C for 5 minutes. (Alternative: React for 10 minutes at room temperature 2-26°C). A solution of urease buffered at pH 6.7 – 6.8 also containing preservative 5. Set the wavelength of the photometer at 630nm and zero the photometer and stabilizers. Avoid contamination. Store at 2-8°C. Exercise the normal with the BLANK. Read and record the absorbances of al vials and proceed precautions required for the handling of al laboratory reagents. Pipetting by to the Calculation with Example below. mouth is not recommended. NOTE: For a direct read-out instrument, set read out to concentration of Standard (25 mg/dl). Read the Unknown concentration directly. A solution containing sodium salicylate, sodium nitroferricyanide and preservative. Avoid contamination. Store at 2-8°C. Do not ingest. Exercise Procedure Notes
the normal precautions required for the handling of al laboratory reagents. Do not pipette by mouth. 1. If a sample exceeds the linearity of the test, make a five-fold dilution of sample with ammonia-free reagent grade water and re-run assay; multiply A solution containing sodium hydroxide and sodium hypochlorite. Avoid 2. If urine is to be assayed; we recommend the use of a diacetyl monoxime contamination. Store at 2-8°C. CORROSIVE! In case of contact, flush affected area with large amounts of water. Seek medical attention. Do not pipette by mouth. Phone: 734-487-8300 • Toll Free: 800-445-9853 • Fax: 734-483-1592 • Urea Nitrogen (BUN)
3. Tietz, N.W., textbook of Clinical Chemistry, W.B. Saunders Co., Philadelphia, Where: A = absorbance, U = UNKNOWN, S = STANDARD, C = p.1270-1271 (1986). 4. Young, D.S. et al, Clin. Chem. 21:1D (1975). 5. Friedman, R.B. et al, Clin. Chem., 26:1D (1975). A (U) x C(S) mg/dl = C(U) mg/dl 6. Laboratory Record. 7. Whitehead, T.P., Quality Control in Clinical Chemistry, John Wiley & Sons, New York (1977). Example: A(U) = 0.31, A(S) = 0.48, C(S) = 25 mg/dl Manufactured for Pointe Scientific, Inc. 5449 Research Drive Canton, MI 48188 0.31 x 25 mg/dl = 16 mg/dl "European Authorized Representative" (O.E.A.R.C.) Av. De Tervueren 34 bte Endpoint Stability
44 B-1040 Brussels, Belgium The final colored reaction product is stable for at least 30 minutes. Procedure Limitations
Sources of error usual y are limited to ammonia contamination of glassware, reagents or atmosphere and fluoride or other potent enzyme inhibitors (i.e. Rev. 5/04 P803-B7551-01 mercury). For a review of drug and disease effects on urea nitrogen values and methods, see references 4 and 5.
Quality Control
Quality control sera should be used routinely to monitor test precision.7
Refer to the manufacturer's package insert for analyte stability and
acceptable limits.
Expected Values3
Healthy Ambulatory Adults ……………. 7-18 mg/dl
These values are suggested guidelines. It is recommended that each
laboratory establish the normal range for the area in which it is located.
Linearity: The method is linear for urea nitrogen values up to 45 mg/dl.
Sensitivity: Typical y, 0.001 A = 0.05 mg/dl in a 1-cm lightpath at 630 nm.
Accuracy: RECOVERY STUDIES (in triplicate)
Within Run
Run to Run

1. Krupp, M.A., Tierney, L.M., Jawetz, E., Roe, R.L., Camargo, C.A., 20th
Ed., Lange Medical Publications, Los Altos, CA, p.216 (1982). 2. Kaplan, A. and Teng, L.L. in Selected Methods of Clinical Chemistry, Vol. 9, Ed. By W.R. Faulkner and S. Meites, AACC, Washington, pp 357-363 (1982). Phone: 734-487-8300 • Toll Free: 800-445-9853 • Fax: 734-483-1592 •


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