Rapid tests for HIV

Diagnostic overview

Laboratory diagnostics of HIV: a brief history

Since the mid-1980’s, HIV diagnosis has been based on laboratory detection of circulating antibodies against HIV. Usually, one screening test was employed followed by a confirmatory test if the initial test yielded a positive result. The ELISA format was the most widely used screening test with a confirmatory test utilizing a western blot or immuno-fluorescent assay (IFA). The ELISA HIV test has undergone a series of iterations that have improved the assay sensitivity which has reduced the diagnostic window period for seroconversion.

Although these tests were highly accurate and economical there still remained unmet needs in the diagnosis of HIV. The process involved an invasive blood draw and the sample was sent to a centralized referral lab where samples had to be batched for analysis, usually by highly skilled personnel. As a result, there was a significant wait time for results. That led to an increase in anxiety for patients as well as significant loss to follow-up for results. The majority of those being tested were further along in disease progression and providing more rapid results would allow for better prognosis with advent of highly active antiretroviral treatment (HAART). Additional benefits of a faster return of patients’ results were a decrease in the stress involved in waiting, a higher return rate, and a chance to impact a person’s behavior to decrease further transmission of the virus. Because these benefits are only useful to patients who know they are HIV positive, increased access to HIV tests is critical. The development of more rapid tests is an important way to increase access to such tests.

Rapid test format

HIV testing needed to be performed outside of the laboratory setting in a more rapid and affordable manner. Therefore, traditional sophisticated methods had to be redeveloped in a format that would have the specifications required for extra laboratory testing.

Rapid HIV test formats that detect antibodies against HIV include:

  • Lateral-flow tests utilize a one-step method in which the patient’s blood specimen is combined with a signal reagent and migrates through a special membrane. A positive reaction is shown as a visible line on the membrane. Most tests take less than 15 minutes. 
  • Flow-through cassettes, or membrane immunoconcentration devices, capture and detect HIV antibodies in a specimen flowing through a porous membrane. A visible dot or line forms on the membrane when HIV antibodies are present.
  • Solid-phase tests include the dipstick “comb” assay. This assay uses a solid plastic matrix to which an HIV antigen is fixed. When HIV antibodies are present, a spot or dot will be visible when processed with a signal reagent.
  • Agglutination tests use different types of particles to produce clumping or settling patterns of the particles when a specimen is positive. An autologous red cell agglutination method detects HIV antibodies with a hybrid antigen-antibody reagent which agglutinates the patient’s red blood cells. A latex particle agglutination detects HIV antibodies by the agglutination of minute latex particles when mixed with the patient’s blood. A newer method uses fluid capillary action to enhance and quicken particle agglutination. Particle adherence detects HIV antibodies when the settling pattern of small gelatin particles is altered.

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