The table below summarizes the most commonly used HIV detection methods, highlighting advantages and disadvantages of each.
|Rapid anti HIV-1/HIV-2 Methods|
- Ease of use
- Can be performed and interpreted while patients are still at the testing site; valuable for patient management, particularly in high prevalence areas and for high-risk individuals.
- Some methods allow alternate specimen types, such as oral fluids or urine.
- High sensitivity, if serum/plasma is used as the specimen type.
- Will only be reactive if antibodies are present.
- Patient may be infectious, but test will be negative, if testing performed during the window period (between infection and a detectable immune response).
- Method is less sensitive if alternate specimen type is used due to less antibody present.
|A neonate should not be tested for HIV by using an anti-HIV method if the mother is seropositive.|
|HIV p24 antigen test|
- Can detect HIV infection before antibodies are produced (between 14 and 22 days post-infection).
- Once antibodies begin to be produced, antigen diminishes below detectable levels.
|Greatest value is in antigen/antibody combination test methods|
|Fourth and fifth generation antigen/antibody combination immunoassay methods (EIA or chemiluminescence)|
- Increased sensitivity over previous test generations. Can detect HIV IgM, which is produced earlier in infection than IgG.
- Combines HIV p24 antigen detection with antibody detection.
- False-positives are possible.
- Usually requires repeat testing if initially reactive and supplementary testing if repeatedly reactive.
|Fifth generation differentiates antigen, HIV-1, and HIV-2 antibodies|
|Western blot (WB)|
- No advantage and no longer recommended as a supplemental test method.
- Results may be indeterminate and require repeat testing at a later time.
- Labor-intensive procedure
- Requires skill and expertise to correctly perform and interpret the results.
| Should not be used as an initial assay due to lower sensitivity than immunoassays |
| Nucleic acid testing (NAT) or |
Nucleic acid amplification testing (NAAT)
- Earliest detection of HIV infection in high-risk seronegative individuals
- Can be used to detect infection in newborns born to HIV-positive mothers
- Specialized training required to perform the assays
- Dedicated laboratory equipment and space required
- False-negative results due to viral suppression are possible
- False-negative results are possible due to improper specimen collection, improper processing, improper storage temperature, or interfering substances in the specimen.
- False-positive results are possible if technical errors occur (eg, amplicon carryover, cross-contamination, inaccurate cutoff values).
|Preferred method for screening blood, plasma, and tissue products. The FDA and AABB require both antibody and NAT testing.|