Diagnosis of Human Immunodeficiency Virus Infection

Abstract

HIV diagnostics have played a central role in the remarkable progress in identifying, staging, initiating, and monitoring infected individuals on life-saving antiretroviral therapy. They are also useful in surveillance and outbreak responses, allowing for assessment of disease burden and identification of vulnerable populations and transmission "hot spots," thus enabling planning, appropriate interventions, and allocation of appropriate funding. HIV diagnostics are critical in achieving epidemic control and require a hybrid of conventional laboratory-based diagnostic tests and new technologies, including point-of-care (POC) testing, to expand coverage, increase access, and positively impact patient management. In this review, we provide (i) a historical perspective on the evolution of HIV diagnostics (serologic and molecular) and their interplay with WHO normative guidelines, (ii) a description of the role of conventional and POC testing within the tiered laboratory diagnostic network, (iii) information on the evaluations and selection of appropriate diagnostics, (iv) a description of the quality management systems needed to ensure reliability of testing, and (v) strategies to increase access while reducing the time to return results to patients. Maintaining the central role of HIV diagnostics in programs requires periodic monitoring and optimization with quality assurance in order to inform adjustments or alignment to achieve epidemic control.

Keywords: CD4; HIV incidence; HIV rapid tests; dried blood spots; drug resistance; early infant diagnosis; enzyme immunoassay; point-of-care testing; quality assurance; viral load.

FIG 1

The tiered laboratory diagnostic network showing the different laboratory tiers, community services, and tests performed at each tier. EID, early infant diagnosis; POCT, point-of-care testing (instrument based). *, HIV RT is the HIV rapid test and refers to strip-like devices.

FIG 2

Historical evolution of serologic assays for HIV diagnosis. Shown are five generations of screening assays using an EIA format for high-throughput processing. Supplemental assays for confirmation of infection used immunofluorescence, WB, and, more recently, simple line or dot immunoassays. Rapid assays for POC testing were initially agglutination tests and later of a lateral flow format and flowthrough design.

FIG 3

Illustration of three supplemental confirmatory assays, Western blotting (WB) (A), the Inno-LIA line blot (B), and the Geenius cartridge (C). WB uses gradient-purified viral lysates as separated antigens impregnated onto nitrocellulose strips. The lateral flow Inno-LIA uses combinations of five and two synthetic or recombinant antigens from HIV-1 and -2, respectively, and the Geenius assay with the dual-path platform (DPP) uses four and two synthetic or recombinant antigens for HIV-1 and -2, respectively. Three and one internal control bands are included in the Inno-LIA and Geenius assay formats, respectively. The banding patterns of a negative specimen and an HIV-1 and -2 dually positive specimen for Inno-LIA is shown in panel B, and the banding pattern of a dually positive specimen for Geenius is shown in panel C.

FIG 4

Methods used for incidence measurement cover pre- or postseroconversion periods. Methods used for preseroconversion specimens include detection of p24 antigen (Ag) and RNA by nucleic acid amplification tests. Methods used for postseroconversion specimens are based on antibody (Ab) maturation and viral genetic diversity. Commercial or in-house assays for the four antibody maturation groups are listed. Assays highlighted in red boxes are methods that use peptides or recombinant antigens derived from multiple subtypes to broaden subtype coverage. Abbreviations: LS, less sensitive; EIA, enzyme immunoassay; BED-CEIA: BED-Capture EIA; IDE, immunodominant epitope; rIDR-M, recombinant immunodominant region of HIV-1 gp41 group M; LAg, limiting antigen; NAT, nucleic acid testing.

FIG 5

Schematic representations of the assay principle for a limiting-antigen (LAg) assay to differentiate low- and high-avidity antibodies (A) and a rapid incidence-prevalence assay (B). (A) At high antigen concentrations, bivalent antibodies of both low avidity (blue) and high avidity (red) bind to microwells coated with antigen, whereas at limiting antigen concentrations, only the high-avidity antibodies bind due to monovalent binding and are retained after washing. (B) Two empirically optimized antigen concentrations are incorporated onto the nitrocellulose strip for diagnosis of HIV infection and detection of recent infection. C, control line; T, test line at a high antigen concentration; LT, low antigen concentration to differentiate recent from long-term infections. The binding of antibody is determined with lateral flow technology. The control band indicated by the arrow is an internal IgG procedural control. Seronegative samples are reactive only for this control band. Persons with recent infections will show C and T lines but not the LT line, and those with long-term infections (>1 year) are reactive to all three lines, including the LT line.

FIG 6

Performance levels from the baseline audit to the 12- to 15-month audit among 968 testing sites in five African countries (Cameroon, Uganda, Malawi, Tanzania, and Zambia) and one Caribbean country (Jamaica). Shown are SPI-RT scores at level 0 (<40%), level 1 (40 to 59%), level 2 (60 to 79%), level 3 (80 to 89%), and level 4 (>90%). The numbers on the top of each bar represent the percentages of the total sites.

FIG 7

Average audit scores (percent) of 968 HIV testing sites in five African countries (Cameroon, Uganda, Malawi, Tanzania, and Zambia) and one Caribbean country (Jamaica) using the SPI-RT checklist on eight quality components.