The Evolution of HIV Testing Continues
Hurt et al. refer to changes in the “official nomenclature” of HIV tests. Although the Centers for Disease Control and Prevention (CDC) does not determine official nomenclature for HIV test types, the CDC Division of HIV/AIDS Prevention has recently made changes to Web sites and other documents that refer to the different types of HIV tests. As discussed at the 2016 HIV Diagnostics Conference,2,3 the term “generations” began to appear in the literature shortly after HIV tests that used recombinant peptides instead of viral lysate antigens (the “2nd generation”) were developed.4–6 However, the “official” nomenclature likely gained traction when Owen et al.7 published an article including a discussion of generations, and CDC and others largely adopted the term for use in presentations, Web pages, and other documents. Indeed, a complete description of test generations appears in both the updated Clinical & Laboratory Standards Institute standards8 and the CDC/Association of Public Health Laboratories (APHL) guidelines for the laboratory diagnosis of HIV infection.9 However, as new HIV tests continued to become available, the lines between generations began to blur. In the 2008 article,7 the term generation was reserved for laboratory-based, instrumented immunoassays. As Hurt et al. reviewed, single-use, point-of-care rapid tests use different technology and probably should be considered separately. Nevertheless, both test manufacturers and authors evaluating these tests began to use the term generations to describe rapid tests. Originally, the generations described incremental improvements in test sensitivity and specificity. However, some of the newer tests within the same generation have different sensitivity for early infection.10 These differences can largely be explained by other aspects of test design, for example, whether they are lateral flow or immunconcentrating rapid tests, reagents used for detection of analytes, or the volume of sample required to perform the test.1 In addition, there are also IgG-sensitive rapid tests that differentiate HIV-1 from HIV-2, and new tests that differentiate p24-antigen detection from antibody detection, but have the same sensitivity during early infection as tests that report only one signal as “reactive for p24-antigen and/or HIV antibody.”1,3,10 As a result, in the article documenting seroconversion sensitivity on plasma specimens that Hurt et al. referenced,10 tests were described in terms of the analytes they can detect and the types of technology (instrumented, laboratory-based, vs. single-use, rapid) that they use to do so. These changes have been implemented in CDC Web pages and documents contained therein.11 In particular, the advantages/disadvantages of Food and Drug Administration–approved HIV tests guide12 may be particularly useful for clinicians and others who need to understand differences in characteristics of the tests available in the United States.
In addition to changing the way we refer to types of HIV tests, CDC has also updated messaging about test window periods.