What is confirmatory testing?

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A confirmatory test is exactly what it sounds like, a test that is used to confirm the results of another test. Many STD testing regimens, such those used for standard HIV testing include built in confirmatory tests, where people getting their test results don't even know that multiple tests may have been done. Confirmatory tests are needed, because STD testing isn't perfect, and in many cases doctors want to be certain that someone has an STD before they diagnose it.

That's particularly true for stigmatized diseases like HIV and Herpes, where a diagnosis can be devastating.

Confirmatory testing can be used to confirm either positive tests -- to make certain someone really is infected -- or negative tests -- to make certain they aren't. The direction is based on which diagnosis is more important to get right. If over-treatment can be dangerous, you want to make certain you don't treat anyone who is really negative for the disease. Similarly, if a false-positive diagnosis could drastically affect someone life, you don't want to tell someone they have something when they don't. That's why the standard regimen for HIV tests involves a very sensitive test followed by a very specific one. The first test is very sensitive, with the goal of detecting every case possible. However, since there's the possibility that could lead to a false positive test, the second test rescreens the blood to make certain no one is diagnosed who shouldn't be.

Rapid Testing & Test Confirmation

One of the trade-offs involved in using rapid tests is that they are sometimes less sensitive than tests that are sent to an outside lab. As such, there may be a somewhat greater need for confirmatory testing in certain situations involving rapid testing. The trade off to that, of course, is that the advantage of rapid testing is that it reduces the need for people to come back in order to get a test result.

In theory, any treatment necessary can start the same day. That works well when treatment is relatively safe and effective and a diagnosis is non-stigmatizing. However, that's not always the case with STDs.

Particularly with HIV testing, it's generally considered better to be safe rather than sorry. That's why some sites that offer rapid testing require confirmatory HIV tests before giving individuals a diagnosis of HIV.  Getting a confirmatory blood test not only helps doctors to be more certain of their diagnosis, it also potentially gives them a chance to assess things such as CD4 count and viral load. Then, if a patient actually does have HIV, the doctor will have more of the information they need to talk about their current health, prognosis, and options for treatment.

Sources:

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Cabié A, Bissuel F, Huc P, Paturel L, Abel S. Impact of rapid HIV testing on the return rate for routine test results in sexually transmitted infection testing centres. Int J STD AIDS. 2011 Dec;22(12):757-8. doi:10.1258/ijsa.2009.009267.

Sacks R, Omodele-Lucien A, Whitbread N, Muir D, Smith A. Rapid HIV testing using Determine™ HIV 1/2 antibody tests: is there a difference between the visual appearance of true- and false-positive tests? Int J STD AIDS. 2012 Sep;23(9):644-6. doi: 10.1258/ijsa.2012.011422.

Zhang D, Meng S, Xu P, Lu H, Zhuang M, Wu G, Liu Y, Pan X, Yan H, Chen X, Fan L, Li C, Fu X, Qi J, Han L, Ma F, Lv F, Sun J. Experience of offering HIV rapid testing to at-risk patients in community health centers in eight Chinese cities. PLoS One. 2014 Jan 28;9(1):e86609. doi: 10.1371/journal.pone.0086609

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