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Human C-Reactive Protein(CRP) ELISA Kit
Catalog No. CSB-E07921h
(96 T)
? This immunoassay kit allows for the in vitro quantitative determination of human CRP concentrations in serum, plasma.
? Expiration date six months from the date of manufacture
? FOR RESEARCH USE ONLY. NOT FOR USE IN DIAGNOSTIC PROCEDURES.
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INTRODUCTION
C-reactive protein (CRP) is a protein found in the blood in response to inflammation (an acute-phase protein). CRP is synthesized by the liver in response to factors released by fat cells (adipocytes). It is a member of the pentraxin family of proteins. CRP is a member of the class of acute-phase reactants as its levels rise dramatically during inflammatory processes occurring in the body. This increment is due to a rise in the plasma concentration of IL-6, which is produced predominantly by macrophages as well as adipocytes. CRP binds to phosphocholine on microbes. It is thought to assist in complement binding to foreign and damaged cells and enhances phagocytosis by macrophages, which express a receptor for CRP. It is also believed to play another important role in innate immunity, as an early defense system against infections. CRP rises up to 50,000-fold in acute inflammation, such as infection. It rises above normal limits within 6 hours, and peaks at 48 hours. Its half-life is constant, and therefore its level is mainly determined by the rate of production (and hence the severity of the precipitating cause). Serum amyloid A is a related acute-phase marker that responds rapidly in similar circumstances. To measure the CRP level, a "high-sensitivity" CRP or hs-CRP test needs to be performed and analyzed by a laboratory. This is an automated blood test designed for greater accuracy in measuring low levels of CRP, which allows the physician to assess cardiovascular risk.
PRINCIPLE OF THE ASSAY
The microtiter plate provided in this kit has been pre-coated with an antibody specific to CRP. Standards or samples are then added to the appropriate microtiter plate wells with a HRP-conjugated antibody preparation specific for CRP to each microplate well and incubated. Then a TMB (3,3’,5,5’ tetramethyl-benzidine) substrate solution is added to each well. Only those wells that contain CRP, HRP-conjugated antibody will exhibit a change in color. The enzyme-substrate reaction is terminated by the addition of a sulphuric acid solution and the color change is measured spectrophotometrically at a wavelength of 450 nm ± 2 nm. The concentration of CRP in the samples is then determined by comparing the
O.D. of the samples to the standard curve.
DETECTION RANGE
0.625 ng/ml-40 ng/ml. The standard curve concentrations used for the
ELISA’s were 40 ng/ml, 20 ng/ml, 10 ng/ml,5 ng/ml, 2.5 ng/ml, 1.25 ng/ml,
0.625ng/ml.
SPECIFICITY
This assay recognizes human CRP. No significant cross-reactivity or interference was observed.
SENSITIVITY
The minimum detectable dose of human CRP is typically less than 0.156 ng/ml. The sensitivity of this assay, or Lower Limit of Detection (LLD) was defined as the lowest protein concentration that could be differentiated from zero.
MATERIALS PROVIDED
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STORAGE
1 Unopened test kits should be stored at 2-8?C upon receipt and the microtiter plate should be kept in a sealed bag with desiccants to minimize exposure to damp air. The test kit may be used throughout the expiration date of the kit. Refer to the package label for the expiration date.
2 A microtiter plate reader with a bandwidth of 10 nm or less and an optical density range of 0-3 OD or greater at 450nm wavelength is acceptable for use in absorbance measurement.
REAGENT PREPARATION
Bring all reagents to room temperature before use for 30min.
1 Wash Buffer If crystals have formed in the concentrate, warm up to room temperature and mix gently until the crystals have completely dissolved. Dilute 20 ml of Wash Buffer Concentrate into deionized or distilled water to prepare 500 ml of Wash Buffer.
2 Standard Centrifuge the standard vial at 6000-10000rpm for 30s. Reconstitute the Standard with 1.0 ml of Sample Diluent. This reconstitution produces a stock solution of 40 ng/ml. Allow the standard to sit for a minimum of 15 minutes with gentle agitation prior to making serial dilutions. The undiluted standard serves as the high standard (40 ng/ml). The Sample Diluent serves as the zero standard (0 ng/ml). Prepare fresh for each assay. Use within 4 hours and discard after use.
3 HRP-conjugate Dilute to the working concentration using HRP-conjugate Diluent(1:100), respectively. The suggested 100-fold dilution can be achieved by adding 10 uL HRP-conjugate to 990uL of HRP-conjugate Diluent for 1ml working solution.
OTHER SUPPLIES REQUIRED
? Microplate reader capable of measuring absorbance at 450 nm, with the correction wavelength set at 540 nm or 570 nm.
? Pipettes and pipette tips.
? Deionized or distilled water.
? Squirt bottle, manifold dispenser, or automated microplate washer.
SAMPLE COLLECTION AND STORAGE
? Serum Use a serum separator tube (SST) and allow samples to clot for 30 minutes before centrifugation for 15 minutes at 1000 x g. Remove serum and assay immediately or aliquot and store samples at -20°C. Avoid repeated freeze-thaw cycles.
? Plasma Collect plasma using citrate, EDTA, or heparin as an anticoagulant. Centrifuge for 15 minutes at 1000 x g within 30 minutes of collection. Assay immediately or aliquot and store samples at-20°C. Avoid repeated freeze-thaw cycles.
Note: Grossly hemolyzed samples are not suitable for use in this assay.
If samples generate values higher than the highest standard, dilute the samples with the Sample Diluent and repeat the assay.
SAMPLE PREPARTION
Normal human serum samples require a 1000-fold dilution into Sample Diluent. The suggested 1000-fold dilution can be achieved by adding 5μl sample to 95μl of Sample Diluent. Complete the 1000-fold dilution by adding 5μl of this solution to 245μl of Sample Diluent. The recommended
dilution factor is for reference only. The optimal dilution factor should be determined by users according to their particular experiments.
As CRP levels increase widely, the patient serum samples are recommended to dilute 1:1000-1:30000 times before test. The recommended dilution factor is for reference only. The optimal dilution factor should be determined by users according to their particular experiments.
ASSAY PROCEDURE
Bring all reagents and samples to room temperature before use. It is
recommended that all samples, standards, and controls be assayed in duplicate.
All the reagents should be added directly to the liquid level in the well. The
pipette should avoid contacting the inner wall of the well.
1 Add 100μl Sample Diluent serves as the zero standard, Add 100μl of Standard or Sample per well. Cover with the adhesive strip. Incubate for 60min at 37°C.
2 Aspirate each well and wash, repeating the process three times for a
total of three washes. Wash by filling each well with Wash Buffer (200μl)
using a squirt bottle, multi-channel pipette, manifold dispenser or autowasher. Complete removal of liquid at each step is essential to good performance. After the last wash, remove any remaining Wash Buffer by aspirating or decanting. Invert the plate and blot it against clean paper towels.
1 Add 100μl of HRP-conjugate working solution to each well. Incubate for 60min at 37°C. HRP-conjugate working solution may appear cloudy. Warm up to room temperature and mix gently until solution appears uniform.
2 Repeat the aspiration and wash five times as before.
3 Add 90μl of TMB Substrate to each well. Incubate for 20 minutes at 37°C. Keeping the plate away from drafts and other temperature fluctuations in the dark.
4 Add 50μl of Stop Solution to each well when the first four wells containing the highest concentration of standards develop obvious blue color. If color change does not appear uniform, gently tap the plate to ensure thorough mixing.
5 Determine the optical density of each well within 30 minutes, using a microplate reader set to 450 nm.
CALCULATION OF RESULTS
Using the professional soft "Curve Exert 1.3" to make a standard curve is recommended, which can be downloaded from our web.
Average the duplicate readings for each standard, control, and sample and subtract the average zero standard optical density. Create a standard curve by reducing the data using computer software capable of generating a four parameter logistic (4-PL) curve-fit. As an alternative, construct a standard curve by plotting the mean absorbance for each standard on the x-axis against the concentration on the y-axis and draw a best fit curve through the points on the graph. The data may be linearized by plotting the log of the CRP concentrations versus the log of the O.D. and the best fit line can be determined by regression analysis. This procedure will produce an adequate but less precise fit of the data. If samples have been diluted, the concentration read from the standard curve must be multiplied by the dilution factor.
LIMITATIONS OF THE PROCEDURE
? The kit should not be used beyond the expiration date on the kit label.
? Do not mix or substitute reagents with those from other lots or sources.
? Any variation in operator, pipetting technique, washing technique, incubation time or temperature, and kit age can cause variation in binding.
? This assay is designed to eliminate interference by soluble receptors, binding proteins, and other factors present in biological samples. Until all factors have been tested in the Immunoassay, the possibility of interference cannot be excluded.
TECHNICAL HINTS
? When mixing or reconstituting protein solutions, always avoid foaming.
? To avoid cross-contamination, change pipette tips between additions of each standard level, between sample additions, and between reagent additions. Also, use separate reservoirs for each reagent.
? When using an automated plate washer, adding a 30 second soak period following the addition of wash buffer, and/or rotating the plate 180 degrees between wash steps may improve assay precision.
? To ensure accurate results, proper adhesion of plate sealers during incubation steps is necessary.
? Substrate Solution should remain colorless until added to the plate. Keep Substrate Solution protected from light. Substrate Solution should change from colorless to gradations of blue.
? Stop Solution should be added to the plate in the same order as the Substrate Solution. The color developed in the wells will turn from blue to yellow upon addition of the Stop Solution. Wells that are green in color indicate that the Stop Solution has not mixed thoroughly with the Substrate Solution.
