HCG ELISA Kit
This immunoassay kit allows for the in vitro quantitative determination of HCG in human serum, plasma and other biological fluids. It is used for diagnosis of early pregnancy.
Human chorionic gonadotropin (HCG) – alpha beta is synthesized by the combined trophoblast cells. The molecular weight of the glycoprotein hormone is 36700. It is composed of two different subunits, alpha and beta. Alpha subunit is similar to FSH, LH and TSH, so intersect reaction happens. While the structure of Beta–subunits are different. Beta-HCG and Beta-LH has similar structure, but the last 24 amino acids are not present in Beta-LH. So the characteristics of beta -HCG subunit were used as a diagnosis to avoid the interference of -LH in clinical application.
HCG appears in the sixth days after fertilization, and can be measured in the serum and urine of pregnant women in the seventh days after fertilization, and it can be used for early pregnancy diagnosis. At 8~10 weeks of gestation, serum concentrations and urine reached a peak, about 50-100kU/L, then it has rapid decline after 10 days. In the middle and late pregnancy, the blood concentration of only 10% to the peak, and sustained to delivery. Generally in the postpartum 1-2 weeks it will disappear. Complete human chorionic gonadotropin is all produced by the placenta chorion syncytiotrophoblast.
Normal Reference Value：Urine-HCG（HCG half quantify）<25IU/L， HCG<100IU/L 。
The LINC-BIO HCG ELISA is a solid-phase, non-competitive immunoassay based on the direct sandwich technique. Calibrator, controls and patient samples are incubated together with anti-HCG monoclonal antibody coated micro titer strips. HCG present in calibrators, controls or samples is absorbed to the microtiter wells during the incubation. The strips are then washed and incubated with horseradish peroxidase (HRP) labeled anti-HCG McAb. After washing , a TMB substrate solution is added to each well and the enzyme reaction is allowed to proceed. During the enzyme reaction a blue colour will develop if antigen is present. The intensity of the colour is proportional to the amount of HCG antigen present in the samples.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. Calibration curves are constructed for each assay by plotting absorbance value versus the concentration for each calibrator. The concentration of HCG in the samples is then determined by comparing the O.D. of the samples to the calibration curve.
Materials and components
- Assay plate 1
- Calibrators 5 x 500ul
With concentrations of 0，5 MIU/ml，20MIU /ml，80MIU /ml，200 MIU /ml
- Anti-hCG-HRP conjugate 1 x 10ml
- Wash Buffer (20 x concentrate) 1 x 30ml
- Substrate Solution 1 x 10ml
- Stop Solution 1 x 5ml
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 approximately 1000 x g. Remove serum and assay immediately.
- Plasma – Collect plasma using EDTA or heparin as an anticoagulant. Centrifuge samples for 15 minutes at 1000 x g at 2 – 8° C within 30 minutes of collection.
- Other biological fluids – Remove particulates by centrifugation and assay immediately。
- Note: Serum, plasma, and cell culture supernatant samples to be used within 7 days may be stored at 2-8 ° C, otherwise samples must stored at -20° C (≤ 3 months) or -80° C (≤ 6 months) to avoid loss of bioactivity and contamination. Avoid freeze-thaw cycles. When performing the assay slowly bring samples to room temperature.
- DO NOT USE HEAT-TREATED SPECIMENS.
Allow all reagents to reach room temperature. All the reagents should be mixed thoroughly by gently swirling before pipetting. Avoid foaming. Arrange and label required number of strips. Prepare all reagents, working standards and samples as directed in the previous sections.
- Add 40 uL of Calibrators, Blank, or Sample per well. Cover with the adhesive strip. Incubate for 40mins at 37° C.
- Aspirate the liquid of each well and wash. repeating the process five times.
Wash by filling each well with Wash Buffer (350 uL) 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.
- Add 100 uL of HRP conjugate solution to each well. Incubate for 40mins at 37°C.
- Aspirate each well and wash, repeating the process five times for a total of three washes. Refer to step2.
- Add 100 uL of Substrate Solution to each well. Incubate for 5-10 minutes at 37°C. Protect from light.
- Add 50 uL of Stop Solution to each well. If color change does not appear uniform, gently tap the plate to ensure thorough mixing.
- Determine the optical density of each well within 10-15 mins, using a microplate reader set to 450 nm.
- 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. When mixing or reconstituting protein solutions, always avoid foaming.
- It is recommended that no more than 32 wells be used for each assay run if manual pipetting is used since pipetting of all standards, specimens and controls should be completed within 5 minutes. A full plate of 96 wells may be used if automated pipetting is available.
- If samples generate values higher than the highest standard, further dilute the samples with the Assay Diluent and repeat the assay. Any variation in standard diluent, operator, pipetting technique, washing technique,incubation time or temperature, and kit age can cause variation in binding.
- The wash procedure is critical. Insufficient washing will result in poor precision and falsely elevated absorbance readings. To ensure accurate results, proper adhesion of plate sealers during incubation steps is necessary.
- This assay is designed to eliminate interference by soluble receptors, ligands, binding proteins, and other factors present in biological samples. 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.
- Duplication of all standards and specimens, although not required, is recommended.
- Do not substitute reagents from one kit lot to another. Standard, conjugate a microtiter plates are matched for optimal performance. Use only the reagents supplied by manufacturer.
Calculation of results
Average the duplicate readings for each calibrator, control, and sample and subtract the average zero standard optical density. Create a calibration curve by reducing the data using computer software capable of generating a four parameter logistic (4-PL) curve-fit or liner curve. As an alternative, construct a calibration curve by plotting the mean absorbance for calibrator on the y-axis against the concentration on the x-axis and draw a best fit curve through the points on the graph. The data may be linearized by plotting the log of the HCG 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.
This assay recognizes recombinant and natural human HCG. No significant cross-reactivity or interference was observed.
Sensitivity The minimum detectable dose of human HCG is typically less than 1MIU/ml.
Detection Range 5MIU/ml –200MIU/ml.
Storage of test kits and instrumentation
- 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 (six months from the date of manufacture). Refer to the package label for the expiration date. Opened test kits will remain stable until the expiring date shown, provided it is stored as prescribed above.
- Do not remove microtiter plate from the storage bag until needed. Unused strips should be stored at 2-8°C in their pouch with the desiccant provided.
- A microtiter plate reader with a bandwidth of 10nm or less and an optical density range of 0-3 OD or greater at 450nm wavelength is acceptable for use in absorbance measurement.
- Substrate Solution is easily contaminated. If bluish prior to use, do not use.
Limitations of the procedure
FOR RESEARCH USE ONLY. NOT FOR USE IN DIAGNOSTIC PROCEDURES.
The Stop Solution suggested for use with this kit is an acid solution. Wear eye, hand, face, and clothing protection when using this material.