Specimens that can be used for ELISA measurement are very wide. Body fluids (such as serum), secretions (saliva), and excreta (such as urine and feces) can be used as specimens to determine certain antibody or antigen components. Some specimens can be directly measured (such as serum, urine), some require pretreatment (such as feces and certain secretions). Most ELISA tests use serum as the specimen. Except for fibrinogen and anticoagulants, other components in plasma are equivalent to serum. The preparation of plasma specimens requires the use of anticoagulants, while serum specimens can be obtained only after the serum naturally coagulates and the blood clots contract.
Except in special circumstances, serum is used as the test specimen in medical tests. Plasma and serum can be used equally in ELISA. Serum samples can be collected according to conventional methods, and care should be taken to avoid hemolysis. When erythrocytes are lysed, substances with peroxidase activity will be released. In ELISA assays labeled with HRP, hemolysis samples may increase non-specific coloration.
Serum specimens should be tested when fresh. If there is bacterial contamination, the bacteria may contain endogenous HRP, which will also produce false positive reactions. If stored in the refrigerator for too long, polymerization can occur, and the background can be deepened in the indirect ELISA. Generally speaking, serum specimens measured within 5 days can be placed at 4 ° C, and cryopreservation should be kept at low temperature for more than one week. After the frozen serum is thawed, the protein is locally concentrated and unevenly distributed. It should be mixed thoroughly and gently, to avoid air bubbles, and the mixture can be inverted upside down. Do not vigorously shake on the mixer. Serum specimens that are cloudy or precipitated should be centrifuged or filtered, and then clarified before testing. Repeated freezing and thawing will make the antibody titer drop, so if the serum samples for antibody detection need to be stored for multiple tests, it should be stored in small quantities in ice. Attention should be paid to aseptic operation when storing serum since collection, and appropriate preservatives can also be added.
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