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Concerning but rare: “False Positives” with Point-of-Care (POC) HIV rapid testing
Jan 31, 2013 by Dr. Sarah Fielden, Manager, BCCDC Point-of-care HIV Testing Program, Clinical Prevention Services, BCCDC
One of my clients had a false positive POC HIV test result. What can I tell my clients to help them deal with this possibility?
Sometimes called “rapid” HIV tests, POC HIV tests are HIV antibody screening tests which can be performed on-site while the client waits, and provide results within minutes. If negative, the HIV test result is considered final (unless acute infection is suspected in which case serology is recommended) but if the POC HIV test is reactive or “preliminary positive” (i.e. two dots), this result needs to be confirmed through standard laboratory testing.
A reactive (preliminary positive) HIV INSTI* POC test result
A preliminary positive POC result can be extremely upsetting for clients and also potentially distressing and disruptive for health care staff. Many health care providers worry about using POC testing because of the increased risk of false positives compared to traditional HIV standard laboratory testing. However, there are also several advantages to POC testing which can include client preference, providing timely results and not requiring follow-up or blood draw on most non-reactive (negative) tests.
Based on clinical trials, the INSTI* test has high sensitivity and specificity of over 99%. However, similarly to other screening tools, in populations with lower prevalence rates of HIV, the POC tests’ predictive ability is reduced. This is why POC testing is most indicated in populations and clients where there is a higher expected prevalence of HIV.
In our experience with the Provincial POC HIV Testing Program with approximately 60 healthcare sites throughout the province, false positives are quite rare. Based on the first 18 months of the provincial POC program and over 17,000 POC tests used for screening, we have report of 9 instances of false positive POC results.
Unfortunately there are no over the counter point-of-care tests that are 100% accurate and errors, although uncommon, may even occur with laboratory testing. Some steps that can be taken for dealing with the possibility of a false positive and mitigating some of the negative impacts on clients and staff are to:
- Integrate the possibility into the HIV pre-test discussions by letting them know that it is a screening test which needs to be confirmed by laboratory testing if reactive and that there is a chance of a false positive result.
- If you have a reactive (“preliminary positive”) result, let the client know that that they could be HIV positive using reassuring language such as “you might be HIV-positive” as part of a comprehensive post-test discussion, especially if there is a lower perceived risk of infection.
- Immediately facilitate confirmatory lab testing by performing or ordering a venous blood sample and have a clear plan in place for connecting the client to support while they wait for their confirmatory HIV test result.
For more information, please refer to the BCCDC POC HIV provincial guidelines and other reference materials at www.bccdc.ca/POC.
* INSTI is the only POC HIV test currently licensed for use in Canada and is manufactured by bioLytical laboratories.
Dr. Mark Gilbert and the BCCDC outreach nurses and STI clinic teams who brought this issue to my attention and for helping to review the information contained herein.
Categories: Clinical tips