window period(redirected from Window Periods)
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See also: incubation period.
In clinical medicine and blood banking, the window period (sense 3 above) refers to the earlier part of the incubation period of an infectious disease, during which the host is or may be infectious to others, but where the presence of infection has not yet caused symptoms and cannot be detected by laboratory testing. Bloodborne viral infections, particularly those due to human immunodeficiency virus (HIV-1) and hepatitis C virus (HCV), can be transmitted sexually, by sharing of needles among intravenous drug abusers, from mother to fetus, by transfusion of blood or blood products, and by accidental needlestick injuries among health care workers. The window periods of these infections are of critical importance in the early detection of transmissible infection in asymptomatic people and in the screening of donor blood. Because those harboring these viruses typically become infectious well before the end of the window period, the challenge is to shorten the period as much as possible by the use of maximally sensitive tests. An important limitation in determining the window period is the difficulty of fixing its beginning, which requires precise knowledge of the time when infection was acquired-often not available except in cases of accidental exposure to body fluids in health care workers, as in needlestick injuries. The definition of the window period has evolved with the emergence of increasingly sensitive tests to detect infection. Early definitions were based on the interval between infection and the appearance of detectable antibody to virus. The development of tests for the presence of viral antigen in plasma shortened the window period, permitting detection of viral material and infectivity before the occurrence of an immune response. Nucleic acid testing, involving detection of viral DNA or RNA after amplification of the specimen by polymerase chain reaction, has reduced the window period for detection of HCV from 82-25 days and of HIV from 22-12 days.
Toxicology The period which corresponds to the interval between ingestion of lethal quantities of a drug or toxin, and development of irreversible organ damage