laboratory markers of HIV infection
Analyses of specimens from seroconversion panels have led to the understanding of HIV-1 viremia after infection and the sequential appearance of different laboratory markers:
- immediately after HIV infection
- low levels of HIV-1 RNA might be present intermittently
- no viral markers can be detected consistently in plasma
- approximately 10 days after infection
- HIV-1 RNA becomes detectable by nucleic acid test (NAT) in plasma and quantities increase to very high levels
- within 4 to 10 days after the initial detection of HIV-1 RNA
- HIV-1 p24 antigens is expressed and quantities rise to levels that can be detected by 4th generation immunoassays
- however this is transient since antibodies begin to develop and bind to the p24 antigen and form immune complexes the interferes with p24 assay detection
- 3 to 5 days after p24 antigen is first detectable (10 to 13 days after the appearance of viral RNA)
- immunoglobulin (Ig) M antibodies are expressed which can be detected by 3rd and 4th generation immunoassays
- finally, IgG antibodies appear and persist throughout the course if HIV infection
The pattern of emergence of laboratory markers is highly consistent. This has led to classification of HIV infection into distinct laboratory stages:
- the eclipse period - period after infection when no laboratory markers are consistently detectable
- seroconversion window period - interval between infection with HIV and the first detection of antibodies.
- acute HIV infection - period between the appearance of detectable HIV RNA and the first detection of antibodies
- established HIV infection - characterized by a fully developed IgG antibody response sufficient to meet the interpretive criteria for a positive Western blot or IFA (1)
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