Immunoassays for the Diagnosis of HIV: Meeting Future Needs by Enhancing the Quality of Testing

Abstract

Immunoassays for detecting HIV infection perform better than other serological assays. HIV immunoassays are presented in a number of different formats: instrument-based, plate, rapid assays and as immunoblots. HIV immunoassays for screening and diagnosis are now in their fourth generation; an assay generation meaning that significant modifications to the assay format have led to a significant enhancement in quality. Although still not perfect, they are now of exceptionally high quality if conducted properly. Most problems relate to how the assays are performed. Many laboratories, especially in high human development index (HDI) countries, manage testing within functioning quality-management systems, but this is not true of laboratories in low HDI countries or in many medium HDI countries. Simple rapid tests for HIV are being used increasingly, and create special challenges for assuring quality. Users of HIV immunoassays are learning that a poorer assay used well has better outcomes than a splendid assay performed poorly. Experience highlights the importance of conducting HIV testing within quality-managed systems and according to international standards, but testing quality and laboratory quality management must be funded adequately.

Human Immunodeficiency Virus Diagnostic Testing: 30 Years of Evolution

“…The assays detected IgG antibody to HIV-1 only. The tests were empirically sensitive but had an antibody-negative window of up to 12 weeks or more postinfection (5). The high sensitivity, while useful for protecting the blood supply, led to false-positive results, especially when low-risk individuals were tested.…”

Human Immunodeficiency Virus

“…In these assays, recombinant HIV-1 and -2 antigens are again attached to the solid phase, but conjugated HIV-1/2 protein antigens rather than conjugated anti-IgG antibodies are used for detection (17). Initially, these assays used enzyme conjugates for detection of bound antigen-antibody complexes.…”

“…These tests are subject to the same limitations as other second-generation assays with a longer "window" period after initial infection when compared to third-or fourth-generation assays; thus, early infections can be missed, leading to false-negative results. Crossreacting antibodies can lead to false-positive results, reinforcing the importance of confirmatory testing (17).…”

HIV Diagnostics: Challenges and Opportunities

“…Quality assurance programs should be in place to evaluate rapid tests before they are put to use, monitor test performance in given geographic regions and develop appropriate algorithms with clear instructions regarding how to proceed with confirmatory testing in the event of an initial positive test result [38][39][40]. In addition, the personnel employing these tests in the field must be properly trained not only in the technical aspects of the assay, since errors in operation or improper interpretation will result in an inaccurate diagnosis, but also to adequately counsel the patient following a diagnosis.…”

“…Compared with assays that detect antibodies alone, Ab/Ag combo assays are more accurate (detecting nearly 90% of infected individuals who had been missed by an initial antibody screening test), able to reduce the diagnostic window period (the time lag between exposure and actual detectable levels of HIV by a diagnostic assay) by almost 7 days because p24 is detectable prior to seroconversion, and may minimize false-negative results in patients carrying strains that vary from endemic circulating forms, since p24 is well conserved [27]. The development of Ab/Ag combo rapid tests will create opportunities for accurate testing in RLS [38].…”