Darko.qxp 13/11/07 11:16 Page 20
HIV & AIDS
Update on the Diagnosis and Monitoring of HIV-1 Infection
a report by
Angela Darko, MD,
1
William Kabat, BS,
2
Niel Constantine, PhD
1,4
and Richard Y Zhao, PhD
1,3,4
1. Department of Pathology; 2. Chicago Children’s Memorial Hospital; 3. Department of Microbiology-Immunology;
4. Institute of Human Virology, University of Maryland School of Medicine
As the HIV/AIDS pandemic continues to progress, it requires rapid and accurate exposure prophylaxis in the injured person within two hours has been shown
diagnostic methods for surveillance, intervention, and monitoring of HIV to dramatically reduce transmission through blood from the source patient.
infections. According to the 2006 HIV/AIDS epidemic update, a total of 39.5 In addition, the rapid tests can be used effectively in outreach settings, public
million people in the world are living with HIV; this is 2.6 million more infections health clinics, and labor/delivery settings where the HIV status is unknown,
than in 2004, and 4.3 million are newly infected cases.
1
Therefore, there is still so that treatment can be given to decrease risk of mother-to-fetal
a need to develop new diagnostic methods that can be used to provide more transmission. As with the EIA methods, results for the rapid HIV test are only
efficient and rapid diagnosis of HIV infection in order to accurately monitor preliminary, require repeat testing to avoid potential technical errors, and
disease progression during antiretroviral therapies, and further to detect early require subsequent testing by a confirmatory method.
emergence of drug-resistant viruses. As the technology continues to evolve, a
variety of new methods are available, many of them approved by the US Food A Western blot or IFA confirmatory test is generally used to eliminate false-
and Drug Administration (FDA) or registered as CLIA (Clinical Laboratory positive results of the screening test. However, a false-negative result may
Improvement Act) waived tests for use in different testing venues. These new also occur if a patient has been recently infected and testing has been
developments include rapid HIV tests that can be used to test urine or oral performed before antibodies are produced—typically less than a week after
fluids, or tests such as automated realtime polymerase chain reaction (PCR) or exposure. In such cases, repeat testing at a later time is required. Despite the
immuno-PCR (iPCR) methods that offer more accurate and sensitive methods outlined advantages of the rapid HIV tests, these tests are currently
of measuring HIV-1 viral load, as well as new methodology that detects early underutilized in some parts of the US because of the lack of adequate
emergence of drug-resistant viruses. With the wide range of new diagnostic resources and availability of these tests, according to the 2006 survey of the
tools available, choosing the appropriate methods for the identification and National Alliance of State and Territorial AIDS Directors (NASTAD).
management of HIV disease will not only lower the costs for the laboratory
testing, but will also allow accurate information to be obtained regarding the There are six commercially available and FDA-approved rapid tests in the US:
patient’s disease status for effective treatment of the disease. Our goal here is the OraQuick Rapid HIV-1/2 Antibody Test (Orasure Technologies, Inc.); the
to briefly outline these methodologies and describe the principles and rationale Reveal G3 Rapid HIV-1 Antibody Test (MedMira, Inc.); the Uni-Gold
for the test, as well as the pros and cons of these diagnostic tools. Recombigen HIV Test (Trinity BioTech); the Multispot HIV-1/HIV-2 Rapid Test
(Bio-Rad Laboratories); the Clearview HIV 1/2 Stat Pak; and the Clearview
Diagnosis of HIV Infection Complete HIV 1/2 (Inverness Medical Professional Diagnostics). The
Some of the classic laboratory methods introduced in the mid-1980s, such as OraQuick is the only FDA-approved test that can utilize oral fluids, finger
enzyme immunoassays (EIAs), Western blot, or indirect fluorescence assays stick blood, venipuncture whole blood, or plasma, and the entire test takes
(IFA), are still widely used for surveillance, blood screening, and diagnosis of about 20 minutes. The Multispot HIV-1/HIV-2 Rapid immunoassay is the
HIV-1 infections. There is a large number and variety of these tests. In only approved test that can differentiate HIV-1 and HIV-2. No other
general, the EIA is used for screening, and Western blot and IFA are for equipment except a timer is needed for the OraQuick, Uni-Gold, and
confirmation of infection.
2,3
A molecular-based nucleic acid test (NAT) has Clearview tests, whereas the other tests require refrigeration and/or
also been approved recently by the FDA for primary diagnosis of HIV-1 centrifugation of blood prior to testing. Molecular-based tests are also used
infection. Most of these tests use serum or plasma for testing, There are FDA- for the screening of blood, particularly for screening the blood donors—
approved EIA methods that are approved for testing urine (HIV-1 Urine EIA, primarily because of their high sensitivity for detecting viral ribonucleic acid
Calypte Biomedical) and oral fluids (Oral Fluid HIV-1 Vironostika MicroELISA (RNA) prior to the appearance of antibodies. In addition, a new RNA-based
System, bioMerieux), and Western blots for urine (Cambridge Biotech HIV-1 NAT was approved in October 2006 for the diagnosis of HIV infection. This
Western Blot, Calypte Biomedical) and oral fluids (OraSure HIV-1 Western test—the APTIMA HIV-1 RNA qualitative test (Gen-Probe)—is now being
blot, Epitope), as well as rapid tests that use multiple sample media. used for diagnosing primary and acute infection, thereby narrowing the
window period in which infection is not detected. It can also be used as a
Rapid HIV tests are easy to use with comparable sensitivity and specificity to confirmatory test for samples that are antibody-reactive by screening tests.
the EIA tests.
3
More importantly, they are cost-effective and useful for private
home testing (not yet allowed in the US) or in situations such as occupational Disease Progression and Therapeutic Responses
exposure when infection status needs to be established for immediate Monitoring HIV disease progression and therapeutic responses is essential for
retroviral treatment. In the case of occupational exposure, initiation of post- the successful treatment and management of HIV-infected patients after
20 © T OUCH BRIEFINGS 2007
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