UREA CE Insert Ref.:27 Intended use. Colorimetric and enzymatic system for urea determination in samples of blood and urine, by end point reaction. Professional use. [Only for in vitro diagnostic use.] Test principle. Urea is hydrolyzed by urease to ammonium ions and CO. Ammonium ions react at alkaline ph with salicylate and sodium 2 hypochlorite, under the catalysator action of the sodium nitroprussiate yielding indophenol blue. The color intensity is proportional to the amount of urea in the sample. Summary. Urea CE Labtest enzymatic-colorimetric system uses the optimized concentrations of reagents, mainly urease, allowing operating with zero order kinetics up to a concentration of 300 mg/dl. It is possible to get a dynamic range very extensive, decreasing notably the repetition of high values tests. The method uses a manual technique and is easily applicable in semiautomated and automated equipments capable of pipetting two reagents and measure with accuracy the absorbance at 580-6 nm. Due to all these reasons, Urea CE Labtest is the chosen method when it is desired to use an enzymatic-colorimetric methodology for urea determination. Methodology. Urease- Labtest Reagents 1. - Urease 2. - Buffer - Store at 2-8 ºC. Reagent label bears expiration date. Phosphate buffer (10 mmol/l) and urease ( 268 KU/L). - Stock - Store at 2-8 ºC. Reagent label bears expiration date. Phosphate buffer (100 mmol/l) ph 6.9, sodium salicylate (312 mmol/l) and sodium nitroprussiate (16.8mmol/L). 3. - Oxidant - Stock - Store at 2-8 ºC. Reagent label bears expiration date. Sodium hydroxide (2.8 mol/l) and sodium hypochlorite (121 mmol/l). 4. - Standard 70 mg/dl - Store at 2-8 ºC. Reagent label bears expiration date. Sodium azide (7.7 mmol/l). In order to avoid evaporation of the Standard, keep the bottle tightly closed. Precautions and warnings For in vitro diagnostic use. Disposal of all waste material should be in accordance with local guidelines. The usual security cares should be applied on the reagent handling. Do not store the reagents near ammonium solutions. The Standard contains sodium azide as preservative. Avoid ingestion. In case of eyes contact, immediately flush eyes with plenty of water and get medical assistance. Sodium azide may react with lead and copper plumbing to form highly explosive metal azides. On disposal, flush with a large volume of water to prevent azide accumulation. Since the volume of sample is small, it is recommended to pipette directly in the bottom of the tube performing a careful measurement in order to minimize the imprecision problems. Water, glass and atmosphere contamination with ammonia may yield false increased results. Avoid smoking in the place where the measurements are performed. Storage and stability. Unopened reagents, when stored at indicated temperature, are stable up to expiration date shown on the label. Deterioration. Microbial or chemical contamination may decrease reagents stability. Specimen collection and preparation Use serum or plasma (Fluorite, oxalate, heparin, EDTA) and urine. Do not use anticoagulant containing ammonia. Fluorite concentration in the sample should not be higher than 3 mg/ml because high concentration inhibits urease. The use of Glistab Labtest (Ref.: 29) is used to collect only one sample for measuring urea, glucose and creatinine. Urea is reportedly stable in serum or plasma for about 12 hours at 15-25 ºC and several days at 2-8ºC.Sampleswithmicrobial contamination should not be used. 24 hours urine should be collected in a container with2.0 ml of 50% HCl and centrifuge before using. Do not use formaldehyde as preservative for urine. No known test method can offer complete assurance that human blood samples will not transmit infectious diseases. Therefore, all blood derivatives should be considered potentially infectious. Interference Urea levels in serum or plasma increase considerably after physical exercises and with age. 01 English - Ref.: 27
In pregnant women, urea levels in serum and urine decrease considerably. Food increases the urea levels in serum or plasma, mainly in women. For therapeutic proposes, it is recommended to collect the samples always at the same time due to the daily variations. Bilirubin up to 32 mg/dl, hemoglobin up to 80 mg/dl and triglycerides up to 900 mg/dl do not interfere significantly. Hemoglobin values higher than 80 mg/dl and triglycerides higher than 900 mg/dl yield positive interferences that can not be minimized using the blank of sample. Materials required not provided 1. A constant temperature water bath (37 ºC). 2. Photometer capable of measuring absorbance at 580-6 nm. 3. Pipettes to measure reagents and samples 4. Timer Preparing the reagents. See note 1 and 2. Buffer in use. Add the content of bottle nº 2 (100 ml) to 400 ml of distilled or deionized water and mix. Stable 12 months in a dark bottle at 2-8ºC. Oxidant in use. Add the content of bottle nº 3 (25mL) to 475 ml of distilled or deionized water and mix. Stable 12 months in a plastic bottle at2-8ºc. The water must have resistivity 1 megaohm.cm, or conductivity 1 microsiemen s/cm and silicates concentration must be <0.1mg/L. Buffered urease: Add 1.0 ml of Urease (nº 1) to ml of Buffer in use. Stable 21 days in a dark bottle at 2-8ºC. Do not store reagents near ammonium solutions. Manual procedure See Precaution and Special Cares. Urine. Dilute the urine 1:50 with distilled water (0.1 ml of urine + 4.9 ml of distilled water) and multiply the result by the dilution factor (50). Set up three tubes and proceed as follows: Mix and incubate in a water bath at 37 ºC during 5 minutes. Oxidant in use Mix and incubate in a water bath at 37 ºC during 5 minutes. Measure the absorbance of the Unknown and Standard against Blank at 600 nm (580-6). The color is stable during 2 hours. The suggested measurement procedure is appropriated to photometer of which the minimal volume of solution for reading is equal or lower than 2.0 ml. It should be done a verification of the necessity of volume adjustment for the photometer to be used. Sample and reagent volume may be modified proportionally without affecting the test performance and the calculation procedure. In case of volume reduction is important to observe the minimum volume needed to the photometric reading. Calibration. The Standard is traceable to NIST SRM 912a. Manual calibrations Calculate the calibration factor weekly. Automatic Systems Blank of reagents: water or 0.85% NaCl; Standards: Calibra Series (Labtest calibrator for automated systems), which are traceable to NIST SRM 912a. Calibration frequency Two or three point calibration after reagent lot change; Two or three point calibration when the internal quality control indicates. Quality control. For quality control use Qualitrol Level 1 and Qualitrol Level 2 or other suitable control material. The limits and control interval must be adapted to the laboratory requirements. Each laboratory should establish corrective actions to be taken if values fall outside the control limits. Calculations. See Linearity. A unknown mg/dl = x 70 A standard Due the great reproductive results of the assays system, it is possible to use the factor method: Calibration factor = 70/A standard Blank Unknown Standard 1.0 ml 1.0 ml 1.0 ml Sample Standard (nº 4) Buffered Urease Blank Unknown Standard 0.01 ml 0.01 ml 1.0 ml 1.0 ml 1.0 ml mg/dl = A Unknown x Factor mg/dl x Urine volume (ml) Urine (mg/24 hours) = 100 Conversion to g/24 hours unit: Urea (g/24 hours) = Urea (mg/24 hours) 1000 02 English - Ref.: 27
Measurement/reportable range Up to 300 mg/dl. If A is higher than 1.0, dilute the colored product and the blank 1:5 Standard with distilled or deionized water. Measure again and multiply the result by 5. Even if after diluting, the value obtained is higher than 300 mg/dl, dilute the sample with 150 mmol/l NaCl (0.85%), measure again and multiply the result by the dilution factor. Dilute the sample so that the obtained value is around 50 and 100 mg/dl. Expected values. Each laboratory should evaluate the transferability of the expected values to its own patient population and, if necessary, estimate its own reference interval. Serum or plasma Age 1 day - 12 months 1-13 years old Children and Adolescents mg/dl 2-34 8-36 Imprecision - Run-to-run Sample 1 Sample 2 Analytical sensitivity. Detection limit: 2.03 mg/dl. The detection limit represents the lowest measurable urea concentration that can be distinguished from zero. It is calculated as two standard deviations of replicates of one sample without urea. Using the Standard Absorbance as parameter, the limit of photometric detection is 0.11 mg/dl, corresponding to an absorbance equal to 0.001. Matrix dilution effects. Two sample with values equal of 74 and 264 mg/dl were used to evaluate the system response on the matrix dilutions with 150 mmol/l NaCl (0.85%). Recoveries were found a range of 99 and 108 %, using dilution factors that vary from 2 to 16. Notes N Mean 24 60 SD 0.30 0.57 %CV 1.3 0.9 Serum or plasma Age Adults Urine. 26-43 g/24 hours. mg/dl 15-45 1. The material cleaning and drying are fundamental factors to the reagent stability and to obtain correct results. 2. The deionized or distilled water in the laboratory to prepare reagents, use in the measurements and for final glass washing must have resistivity 1 megaohm.cm, or conductivity 1 microsiemens/cm and silicates concentration must be <0.1mg/L. Conversion. Conventional Unit x 0.166 = IS Unit (mmol/l). Performance characteristics 7 Recovery studies. In two samples with urea concentrations of and 50 mg/dl were added different quantities of the analyte. Subsequent analyses provided recoveries ranging from 97 to 100%. The mean proportional systematic error at 60 mg/dl decision level was 0.9 mg/dl or 1.5 %. Method comparison. A group of 40 sera were assayed by the proposed method and a similar technique. Serum urea values ranged from 17-116 mg/dl. The comparisons yielded a correlation coefficient of 0.998 and regression equation was y = 1.147 + 0.973x. The mean proportional systematic error at 60 mg/dl decision level was 0.47 mg/dl or 0.78 %. 3. It is suggested to consult Young DS. Effects of Drugs on Clinical rd Laboratory Tests, 3 Edition, Washington: AACC Press, 1990. in order to review physiopathological source and drugs interference in results and methodology. References rd 1. Bergmeyer HU. Methods of Enzymatic Analysis, v. 8, 3 ed., Deerfield Beach: Verlag Chemie, 1985; 444 49. 2. Bollet WT, Bushman CJ, Tidwell PT. Anal Chem 1961;33:592-594. 3. Tonks DB. Quality Control in Clinical Laboratories, Warner-Chilcott Laboratories, Diagnostic Reagents Division, Scarborough, Canada, 1972. 4. Weatherburn MW. Anal Chem 1967;39:971-974. Imprecision - Within run Sample 1 Sample 2 N Mean 24 60 SD 0.12 0.48 %CV 0.5 0.8 5. Westgard JO, Barry PL, Hunt MR, Groth T. Clin Chem. 1981, 27:493-501. 6. Soldin SJ, Brugnara C, Wong EC: Pediatric Reference Ranges, 5a. edição, Washington: AACC Press, 05: 195-196. 7. Labtest: data on file. 03 English - Ref.: 27
Presentation Product Reference Contents Urea CE 27-500 Application procedures using Urea CE are available for various automated systems. The number of testes in automated systems depends of the programmed parameters. 1 2 3 1 x 25 ml 1 x 100 ml 1 x 25 ml 1 x 3 ml Customer information [Warranty conditions] Labtest Diagnóstica warrants the performance of this product under the specifications until the expiration date shown in the label since the application procedures and storage conditions, indicated on the label and in this insert, have been followed correctly. Labtest Diagnóstica S.A. CNPJ: 16.516.296 / 0001-38 Av. Paulo Ferreira da Costa, 600 - Vista Alegre - CEP 33400-000 Lagoa Santa. Minas Gerais Brasil - www.labtest.com.br Customer Service e-mail: customerservice@labtest.com.br Revision: October, 14 Ref.: 100717 Copyright by Labtest Diagnóstica S.A. Reproduction under previous autorization 04 English - Ref.: 27
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