Window phase of infection

Question

What is the window phase of infection? How is this concept significant for the test of HIV infection in the blood banks?

Answer 1

The main immune response of body facing any infection is not immediate. The window phase is period from the infection till the formation of detectable particular antibodies against the infective agent.

In this time, immunochemical tests that not directly search infections, such as the ELISA and the Western-blot for HIV, give a negative result even if the person is really infected by agent. In the case of HIV, the window phase can last regarding 2 weeks to 3 months. The window phase is a vital problem for blood banks which perform only immunochemical tests on the donated blood. This is the reason why in some countries blood donors are submitted to a sequence of questions regarding their prior behavior, mainly sexual and drug use related, in months previous the donation and also to voluntary confidential self prohibiting, in that they declare whether their blood might be employed or must be excluded. Instead of facing this hazardous problem, modern blood banks nowadays employ PCR (or polymerase chain reaction) for HIV, a test which is not distorted by window phase as it is not antibody-based.

Using particular primers, the PCR detects the presence of the DNA generated by the reverse transcription of HIV RNA.