There is usually a period of several weeks in which newly infected people have not yet produced enough HIV antibodies to be detected. The CDC said there have been 35 AIDS cases since 1985 linked to blood from people in this "window period."
Like the first generation of AIDS blood tests, current tests detect antibodies to the AIDS viruses. Unfortunately, for a brief time after infection, people make too few antibodies for these tests to detect. As a result, their blood passes all the screening tests, even though it can transmit HIV. The "window period" for HIV-1 lasts about 22 days The FDA recommended in August 1995 that blood banks begin using the new p24 antigen test for HIV-1 when it became available. This test might cut 6 to 12 days from the window period=97at an added cost of perhaps $60 million each year.
Future tests may be based on the polymerase chain reaction (PCR), which can detect HIV directly by detecting its genetic material. PCR is sensitive enough to detect HIV in blood several days earlier than the p24 antigen test. PCR was invented in the mid-1980s, and it gave scientists a way to quickly and simply make millions of copies of genes for their experiments. Molecular biologists could probe the gene defects underlying cystic fibrosis, muscular dystrophy, and many other diseases.
Virologists could study the myriad variants of HIV-1 to determine how the virus changes over time. Pharmacologists could measure the effects of potential drugs on viruses. Archaeologists could track ancient human migrations . Once refined by experimental scientists, PCR was eagerly adapted by clinicians. Its sensitivity made it seem a natural for testing donated blood for diseases.
So far, PCR has proved difficult to automate, a necessity for processing the 14 million units of blood donated each year. Also, PCR is expensive and, as viewers of the O.J. Simpson trial learned, demands pristine handling conditions and meticulous technique. More research is needed before blood banks can take advantage of PCRs power. But protecting the blood supply from HIV-1 is not enough. Scientists continue to discover other diseases that can be transmitted in blood. Also, mistakes can occur. Blood can be mislabeled. Blood bank volunteers can neglect to ask prospective donors all the required questions. Lab workers can be sloppy in testing blood, or a test kit can be defective. Thousands of errors and accidents are reported to FDA each year.
And even if cheap, reliable, error-proof screening tests were available for every transmittable disease, transfusion would still not be 100% safe. No medical procedure is . Transfusions cause some kind of problem in about 10% of recipients. These problems range from fever and hives to iron overload and congestive heart failure.
The test, to be sold under the name Abbott HIVAG-1 Monoclonal, is an enzyme immunoassay (EIA), and is the second FDA-licensed HIV antigen detection kit intended for use in blood banks and plasma centers nationwide according to new FDA blood screening recommendations. Abbott HIVAG-1 Monoclonal is also cleared for prognostic use in HIV-infected patients.
"The test reduces the window period between HIV infection and detection the first 25 to 45 days, when the virus can elude efforts to screen it out," said Ronald Gilcher, M.D., president and CEO, Sylvan N. Goldman Center, Oklahoma Blood Institute, where the test has been researched since 1991. "The new test also cuts testing time to four hours from 24 from Abbotts earlier version antigen test."
HIV antibody testing has been used by all U.S. blood institutions to screen donated blood and plasma for HIV infection. This new test will allow U.S. blood screening centers to have an alternate source for the p24 antigen test. (HIV antibody tests will continue to be used in parallel to identify HIV positive blood.) While antibody testing can measure the bodys immune response to the presence of a virus, antigen testing detects the virus itself. Patients infected with HIV may have positive antigen results very early in the infectionbefore a substantial antibody response has formed. As a result, people recently infected with HIV may be identified by the antigen test while the antibody test remains negative or indeterminate until a later date.
I hope this information is of some assistance.David A. Reznik, D.D.S. Some notes and a link The "window period" is the time it takes for a person who has been infected with HIV to react to the virus by creating HIV antibodies.
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Local factors in the genital tract are also important. Other local infections, ulcers, mucosal trauma etc contribute of higher chance. Prophylaxis with medicines can prevent transmission if taken as early as possible after exposure, preferably within a day of contact. Medicines are not of known benefit after 1 month. PCR test can confirm the disease early after contact (95% detection after 6 weeks). ELISA and Western blot can be falsely negative upto 3-4 months. Similarly, a negative test in the sex worker may not mean 100% negative result, if the lady is in window period. If you are negative even after 6 months, means you should have not acquired the infection. In such a fortunate situation, it is wise to avoid sexual mis-adventures in future!
Your WB test is negative at this point (nearly 50 days; less than 2 months). It is most likely that you are un-infected. However, as a possibility of still 5-10% chance, it is worthwhile to not donate blood for 6 months post exposure. A negative WB or ELISA at 3 months will however make you 99% negative and at 6 month, 100% negative. If there is an emergency to donate, a negative DNA PCR test at this point can be done which can suggest that you are 99% negative.Dr AS, AIDSHELPLINE Belgaum, India
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