Since 1985, when the first HIV antibody test was approved in the U.S., HIV antibody testing technology has been updated with the rapid development of immunology and molecular biology techniques. According to the “National HIV Testing Technical Specification” issued by the Ministry of Health in 2004, HIV antibody testing is divided into three steps: initial screening, retesting and confirmatory testing.
1.Primary screening and retesting test.
It mainly includes enzyme-linked immunosorbent assay, rapid detection test, chemiluminescence immunoassay, time-resolved fluorescence immunoassay technique and non-invasive HIV antibody test.
1.1 Enzyme-linked immunosorbent assay (ELISA).
HIV antibody ELISA reagents have gone through four generations.
In 1985, the first generation of indirect ELISA, HIV virus lysate as the envelope antigen, sensitivity and specificity is not high, the window period of about 3 months; 1990, the second generation of indirect ELISA, genetically engineered recombinant or synthetic peptide as the envelope antigen, can detect HIV-1 and HIV-2 at the same time, the specificity has greatly improved compared with the first generation, the window period was shortened by about 20 days; 1994, the third generation of dual antigen sandwich method The 3rd generation dual antigen sandwich method, the same as the 2nd generation, but the new gp41 peptide, can detect a variety of HIV antibody subclasses including IgG, IgM, IgA, etc., the sensitivity and specificity is higher, the window period is shortened to 3-4 weeks, is the current mainstream products; 1998, the 4th generation, HIV antigen and anti-p24 antibody coated solid phase carrier, can detect HIV antibody and p24 antigen at the same time, the sensitivity is further improved, “the window period is shortened to about 20 days. The sensitivity is further improved and the “window period” is further shortened by 4-8d, but there is a “second window period”, which is currently used for auxiliary diagnosis.
1.2 Rapid test (RT).
Including immunospot test, immunochromatographic test, gelatin particle agglutination test. The method is simple: no special equipment is needed, rapid: test results can be obtained within 30 min, especially for emergency testing, HIV surveillance sentinel sites, township health centers and community health stations, etc.
1.3 Chemiluminescence immunoassay.
Microparticle, microplate chemiluminescence immunoassay technology to detect HIV antibodies, with higher sensitivity than ELISA. The electrochemical chemiluminescence immunosensor constructed by mesoporous materials loaded with quantum dots and encapsulated with nanogold can detect HIV antibodies with high selectivity and sensitivity.
1.4 Time-resolved fluorescence immunoassay technique.
The application of double antigen sandwich combined with time-resolved immunofluorescence analysis (europium-labeled HIV antigen) has greatly improved the sensitivity and specificity. The sensitivity of the kit is 100%, the specificity is 98.9%, and the accuracy is 99.4%.
1.5 Non-invasive HIV antibody test.
In addition to blood testing, saliva and urine testing has become a new means of HIV testing, which has more advantages in terms of safety and convenience.
2. Confirmatory test.
HIV antibody screening positive samples need to confirm the test, mainly immunoblot test, strip immunoblot test, also includes radioimmunoprecipitation test and immunofluorescence test, etc.
2.1 Immunoblot test (WB).
WB is currently the most commonly used method for HIV positive confirmation in China, and the combination of ELISA + WB is the recognized gold standard for HIV diagnosis. The basic principle is to electrophoresis of HIV whole virus antigen by SDS-PAGE and then electrotransfer to NC membrane; add the serum to be tested, then add the enzyme-labeled anti-human IgG and substrate to present a band at the corresponding position of the membrane that can be discerned by the naked eye.
2.2 Strip immunoblotting assay (LIA).
LIA is a modification of WB method, using genetically engineered recombinant protein or chemically synthesized peptide to replace the antigen of viral lysate used in WB method as the antigen of diagnostic reagent.