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These modifications are catalyzed by polymerases, ligases, nucleases, phosphatases, and methylases, respectively.An arsenal of laboratory methods is available to screen blood, diagnose infection, and monitor disease progression in individuals infected by HIV.
Tests to detect antibody to HIV can be further classified as: 1) screening assays, which are designed to detect all infected individuals, or 2) confirmatory (supplemental) assays, which are designed to identify individuals who are not infected but who have reactive screening test results.
Accordingly, screening tests possess a high degree of sensitivity, whereas confirmatory assays have a high specificity.
Regardless of the particular screening test used, serum or plasma samples first are tested (screened) using a test with high sensitivity, most often an enzyme-linked immunosorbent assay (ELISA), "rapid test," or "simple method" (described below).
ELISA is the screening method used most commonly, with the other 2 methodologies offering more rapid results with simple procedures applicable for use in point-of-care testing and in developing countries.
The diversity of potential applications has conducted to the development of lytic enzyme systems with specific characteristics, suitable for satisfying the requirements of each particular application.
Nucleic acids used for molecular cloning can be of natural or synthetic origin, and their length ranges from a few to several thousands nucleotides.Biotechnology could be traced back to thousands of years ago when human started to use yeasts to make liquor.This may be the first dawn of biotechnology in food production.Tests with high sensitivity produce few false-negative results, whereas tests with high specificity produce few false-positive results.These classes of assays, performed in tandem, produce results that are highly accurate, reliable, and appropriate to protect the blood supply or assist in the diagnosis of HIV infection.The use of such antigens allows HIV screening tests to possess both sensitivity (to detect infection) and specificity (to detect noninfection).In the United States, screening tests for HIV must be licensed by the Food and Drug Administration (FDA), regardless of whether they are used for screening blood, diagnosis, or monitoring disease.With the advent of new therapies to treat HIV infection and the recommendation to institute therapy as soon as possible (but no later than 72 hours) after exposure,(5) rapid assays may be the most appropriate for testing the source patient after exposure (eg, needlestick injuries).More recently, tests have been developed using fluids that can be obtained conveniently outside the clinical laboratory.Using the early-generation tests, antibody could be detected in most individuals by 6 to 12 weeks after infection.Newer-generation assays, including the third-generation antigen sandwich assays, can detect antibody at about 3-4 weeks after infection.(2) This window period before the detection of antibody can be shortened by several days using antigen tests, and by several more days using nucleic acid detection methods.(3) Therefore, in most individuals, the window period may be only 2-3 weeks if an all-inclusive testing strategy is used.