HIV Testing non-reactive, no further testing is required. However, in some cases where there has been a suspected recent high-risk exposure to HIV, laboratory testing can be used to confirm the negative result[5].
EIA Tests EIA tests, also know as ELISA tests, refer to enzyme immunoassay tests, which detect antibodies to HIV[4]. Window periods vary for these tests based on test generation. In antibody-based tests, it is important to be aware of whether the HIV test covers HIV-2 in addition to HIV-1, if an HIV-2 infection is suspected[1]. • 3rd generation EIA detect both IgM and IgG antibodies within approximately 6 to 12 weeks[1,4] • 4th generation (combined) tests combine a test for p24 viral antigen with a 3rd generation HIV antibody test[1,4] P24 antigen levels are detectable in most people by 20 days after infection. However, they being to decline within 3 to 4 weeks after infection and are no longer detectable by 5 to 6 weeks post-infection[4]. Anti-HIV antibodies are detectable after the window period (approximately 6 to 12 weeks) and remain detectable throughout the trajectory of HIV infection. HIV infection is detectable in “50% of people by 18 days after infection, 95% of people by 34 days and 99% of people by a month and a half[4].”
14 days). However, their high cost limits their use and accessibility, and they are may be primarily used for testing among higher-risk populations[4].
P24 testing Exclusive p24 antigen testing is another testing option that can be used as a confirmation test following a nonreactive rapid test result[4].
Self-Testing Kits Self-testing for HIV can either be supervised and restricted to clinic use or distribution by community health care workers, or can be non-restricted and unsupervised with open access (home-testing kits)[6]. Self-testing kits can either be blood-based (finger-prick) or using oral fluid (e.g. OraQuick In-Home HIV Test)[5,6]. Advantages to self-testing kits include decreased barriers related to stigma and discrimination and improved accessibility to testing[6]. However, there are legal concerns about disclosure of HIV self-testing results depending on national laws, accurate interpretation of test results and ensuring access to appropriate counselling and treatment[5,6]. Overall, accuracy and acceptability for HIV self-tests are high, with blood-based tests have a higher sensitivity and specificity than oral fluid tests[6]. HIV self-tests should also be considered a screening test and not a first-line assay and are only accurate outside of the 6 to 12 week window period[5].
Western Blot Tests Western Blot tests are an antibody-based and are often used to confirm reactive results from an ELISA or rapid HIV tests. They have the longest window period (approximately 2 months), are more expensive and require more skilled training[1,4]. However, their specificity is higher and therefore their utility lies in ruling out falsepositive results from the more sensitive yet less specific EIA tests.
NAAT Testing NAAT testing detects small quantities HIV nucleic acid (e.g. DNA and RNA) and has the shortest window period of all HIV test types (a window period of 7 to 6
1. World Health Organization. Consolidated Guidelines on HIV Testing Services. Geneva: WHO Press; 2015 [cited 2016 November 5]. Available from http:// apps.who.int/iris/bitstream/10665/179870/1/9789241508926_eng. pdf?ua=1&ua=1 2. UNAIDS. Press Report. 2014. Available from http://www.unaids.org/ en/resources/presscentre/pressreleaseandstatementarchive/2014/ july/20140716prgapreport 3. Wilton, J., & Broeckaert, L., The HIV treatment cascade – patching the leaks to improve HIV prevention. CATIE: 2013 [cited 2016 November 5]. Available from http://www.catie.ca/en/pif/spring-2013/hiv-treatment-cascade-patching-leaksimprove-hiv-prevention 4. Wilton, J. HIV testing technologies. CATIE: 2015 [cited 2015 November 5]. Available from http://www.catie.ca/en/fact-sheets/testing/hiv-testingtechnologies 5. Broeckaert, L., & Challacombe, L. Rapid point-of-care HIV testing: A review of the evidence. CATIE, 2015 [cited 2016 November 5]. Available from http:// www.catie.ca/en/pif/spring-2015/rapid-point-care-hiv-testing-review-evidence 6. UNAIDS. A short technical update on self-testing for HIV. WHO Press: Geneva, 2014 [cited 2016 November 5]. http://www.unaids.org/sites/default/ files/media_asset/JC2603_self-testing_en_0.pdf
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