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Creatinine Reagent

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Creatinine Reagent Creatinine Reagent ® INTENDED USE 3. Do not use washed cuvettes. FOR IN VITRO DIAGNOSTIC USE 4. Avoid contact of reagent with eyes, skin and clothing. Do not pipette reagents by Creatinine Reagent is intended for the quantitative determination of creatinine in serum, mouth. Do not ingest. Wash hands after use. plasma and urine. 4. Corrosive (Sodium hydroxide.) Causes burns. In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. Wear suitable gloves and SUMMARY eye/face protection. In case of accident or if you feel unwell, seek medical advice Serum creatinine is a waste product formed by the spontaneous dehydration of body immediately creatine. Most of the body creatine is found in muscle tissue where it is present as SPECIMEN COLLECTION creatine phosphate and serves as a high-energy storage reservoir for conversion to Either serum, EDTA, lithium or sodium heparin plasma or urine may be used with the adenosine triphosphate. The rate of creatinine formation is fairly constant with about 2 appropriate system parameter settings. 1 percent of the body creatine being converted to creatinine every 24 hours. Serum Sample collected by standard technique. Creatinine in the serum or plasma sample is creatinine and urea levels are elevated in patients with renal malfunction, especially 8 stable for 24 hours at 2-8°C. Creatinine in the urine sample may be stored at 2-8°C for 4 decreased glomerular filtration. A single, random measurement of serum creatinine may days.8 Both samples may be frozen for longer storage. be used as an indicator of impaired kidney function. In the early stages of kidney damage, the rise in the serum urea levels usually precedes the increase in serum creatinine. This INTERFERING SUBSTANCES advantage is offset by the fact that serum urea levels are affected by factors such as diet, The following compounds at the indicated levels gave less than 0.1 mg/dL interference as degree of hydration, and protein metabolism. Conversely, serum creatinine levels tend to apparent creatinine when added to a normal serum pool. be constant and unaffected by factors affecting serum urea levels. Thus serum creatinine is a significantly more reliable renal function screening test than serum urea.2 A acetoacetic acid 20 mg/dL considerably more sensitive test for measuring glomerular filtration is the creatinine acetone 25 mg/dL 1 clearance test. For this test, a precisely timed urine collection (usually 24 hours) and a ascorbic acid 10 mg/dL blood sample are needed. Urine creatinine levels, as well as other markers of dilution, i.e., albumin 3 g/dL specific gravity and appearance, are useful as an adjunct to drug abuse testing in fructose 200 mg/dL determining external dilution or excessive donor hydration.3,4 Most creatinine assays are glycerol mg/dL based on a modification of the original Jaffe reaction.5 In many of these procedures, the 30 sample is added to an alkaline picrate solution, and the absorbance is read after the glucose 500 mg/dL reaction has reached end point. Although relatively simple and convenient, the end point hemoglobin 10 g/L assays are somewhat non-specific and subject to interferences by serum metabolites. β - hydroxybutyrate 10 mmol/L Improvements in the end point assays have been made by using cation-exchange resins pyruvate 0.2 mmol/L 6 and Lloyd‘s reagent to remove the creatinine from the sample. Though effective, these uric acid 20 mg/dL procedures are time consuming and require centrifugation or filtration steps. More recently, kinetic assays using the Jaffe reaction have been developed to increase the Cephalosporin antibiotic interferences with Jaffe methods for creatinine have been specificity for creatinine and to reduce the interference by serum metabolites.7 described.10 When tested at the concentrations indicated below, the following PRINCIPLE OF PROCEDURE cephalosporin antibiotics spiked into serum containing a level of 1.0 mg/dL creatinine The Creatinine Reagent uses a kinetic modification of the Jaffe reaction. were found to give the amount of interference indicated: Cefaclor at 100 mg/dl showed an increase of 0.7 mg/dL. Alkaline Cefoxitin at 100 mg/dl showed an increase of 5.3 mg/dL. Creatinine + Picric Acid red complex Cephaloridine at 100 mg/dl showed an increase of 1.2 mg/dL. pH Cephalothin at 100 mg/dl showed an increase of 0.2 mg/dL. The rate of formation of the red colored complex is measured at 500 nm on the COBAS Intralipid at 1000 mg/dL (representative of lipemia) caused a negative 0.2 mg/dL ® MIRA and is proportional to the creatinine concentration in the sample. On COBAS interference at a creatinine level of 1.5 mg/dL. Urea at 1000 mg/dL caused a positive 0.2 instruments, a time interval for measuring the reaction is chosen to minimize non- mg/dL interference at a creatinine level of 1. 2 mg/dL. creatinine interferants. Bilirubin interference as apparent creatinine was tested using both conjugated and REAGENTS unconjugated bilirubin spiked samples. For every 1.0 mg/dL of unconjugated bilirubin Reactive ingredients present in the sample, an apparent loss of 0.03 mg/dL creatinine was observed. For every Reagent 1 1.0 mg/dL of conjugated bilirubin (ditaurobilirubin) present in the sample, an apparent loss Sodium Borate 215 mmol/L of 0.08 mg/dL creatinine was observed. Thus, care should be taken in the interpretation of pH 13.1 low creatinine values when high levels of bilirubin are present. Less than 10% interference was demonstrated from up to 600 mg/dL Hemoglobin F. Reagent 2 Young gives a list of drugs and other substances that interfere with the determination of Picric Acid 52 mmol/L creatinine.11,12 Sodium Borate 35 mmol/L pH 8.0 PROCEDURE Nonreactive ingredient Materials provided Stabilizers R85559 R85559V1 R1 2 x 100 mL The final reaction mixture contains R85559V2 R2 2 x 100 mL Sodium Borate 96 mmol/L Picric Acid 20 mmol/L R85546 R85546V1 R1 10 x 3 mL pH 13.0 R85546V2 R2 10 x 3 mL Nonreactive ingredients Materials required but not provided Stabilizers 1. COBAS MIRA® chemistry analyzer. REAGENT PREPARATION 2. Multi-Analyte Serum Calibrator (R60010) Mix equal volumes of the Reagent 1 and Reagent 2 prior to use. TEST PROCEDURE 30 oC Pour sufficient working reagent into the proper position on the reagent rack and place on 15 oC STORAGE AND STABILITY the instrument. R85546 contains vials that are COBAS MIRA® system rack compatible. Store the reagents at 15-30 °C. The reagents are stable until the expiration date on the See appropriate operator’s manual for further details on system programming and label. Keep reagent bottles tightly closed when not in use. Once opened, Reagent 1, operation. Reagent 2, and combined (working) Creatinine Reagent are stable for 21 days when stored in a tightly closed container and 6 hours when exposed to atmosphere. Discard CALIBRATION the reagent if it appears turbid or fails to recover stated values for the control sera. Use Multi-Analyte Serum Calibrator (R60010) for serum samples. Consult the package Reagent 1 should be clear and colorless; Reagent 2 and the working reagent should be insert for this product for instructions on use. Calibrate in accordance with the instrument clear and yellow in color. manufacturer’s specifications. Calibration stability is dependent upon the instrument performance and the proper storage of the reagents. Re-calibration is recommended at WARNINGS AND PRECAUTIONS anytime, should one of the following occur. 1. Good laboratory safety practices should be followed when handling any 1. Change in the reagent lot number. laboratory reagent. Refer to a recognized laboratory safety program for 2. Preventative maintenance is performed on the analyzer. additional information. (See GP17-T, Clinical Laboratory Safety; Tentative 3. A critical element of the analyzer is replaced. Guideline (1994), National Committee on Clinical Laboratory Standards, 4. Control material results have shifted or are out of range and the use of a freshly Wayne, PA.) reconstituted vial of control does not correct the situation. 2. Results should be interpreted considering all other test results and clinical Each laboratory should establish its own procedures for corrective action if status of the patient. calibration is not acceptable. 32490_05 10/16/12 © 2008 Cliniqa Corporation. All rights reserved. QUALITY CONTROL The following table lists the data obtained in a comparison of urine samples with the Controls are recommended to monitor the performance of manual and automated assay reagent for Creatinine (y) with a similar creatinine reagent (x) run on a COBAS MIRA®. procedures, providing a continued screening of the instrument, reagents and techniques. Number of sample pairs (n) 56 Assayed Control Serum Level 1 (R83082) and Assayed Control Serum Level 2 (R83083) Slope 0.94 are recommended for this purpose. Each laboratory should establish its own control y-Intercept -0.694 schedule. Correlation coefficient 0.998 CALCULATIONS Precision COBAS chemistry instruments calculate a factor using the following formula: Precision studies using control sera were performed on a COBAS MIRA according to the 1 CSTD11 CSTD21 13 F= - + guidelines of NCCLS Publication EP5-T. 2 ∆A - ∆A ∆A - ∆A STD11 RB STD21 RB Total Within Run Mean (mg/dL) CV% CV% then: Level 1 4.0 2.7 1.6 Concentration of the sample (mg/dL) = (∆ASample - ∆ARB) x F Level 2 9.4 2.0 0.5 where: C = Concentration in mg/dL Urine specimens with low and high concentrations of creatinine on a COBAS MIRA STD11 = Standard One (first replicate) showed the following performance: STD21 = Standard One (second replicate) Total Within Run ∆A = Absorbance Change Mean (mg/dL) n CV% CV% RB = Reagent Blank Level 1 72.7 20 3.6 3.6 F = Factor Level 2 136.3 20 4.5 2.5 CREATININE CLEARANCE The creatinine clearance is calculated using the following formula: EXPECTED VALUE U 1.73 A study was conducted on a total of 100 samples from normal blood donors (52 females Creatinine clearance (mL/min) = x V x and 48 males) using the Creatinine Reagent.
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