American Association for Clinical Chemistry
Better health through laboratory medicine
January 2009 Clinical Laboratory News: HIV Screening

 

January 2009: Volume 35, Number 1


HIV Screening
A Look at the CDC Guidelines and HIV Rapid Tests
By Patricia Slev, PhD

 

 

In 2006, approximately 25% of the 1 million individuals infected with HIV in the U.S. were unaware of their HIV-positive status. In an effort to increase awareness and promote early diagnosis of HIV infection, the CDC responded to this public health epidemic by releasing revised recommendations for HIV screening of adolescents, adults, and pregnant women. The guidelines, published in September 2006, not only expanded HIV screening to individuals age 13–64 in all routine healthcare settings, they also eliminated the need for special consent forms or prevention counseling (1).

Identifying infected individuals is critical for two reasons. First, undiagnosed individuals miss the opportunity to receive timely, highly active antiretroviral therapy that now allows people to live with HIV as a chronic disease (2). In addition, undiagnosed individuals are disproportionately responsible for new infections. According to CDC reports, 25% of individuals who are unaware of their infection are responsible for 54%–70% of new HIV infections (3). This is important because studies show that individuals who are aware of their infection status reduce behaviors that contribute to HIV transmission (4). Despite these statistics, the most common reason that people seek testing for HIV on their own remains overt illness. Surprisingly, most of these individuals have sought medical attention multiple times for unrelated complaints in a variety of healthcare settings prior to being tested and diagnosed with HIV.

While implementation of the CDC guidelines across the U.S. is still limited, studies have emerged that provide important data on the benefits of expanded HIV screening. This article will describe some of those studies, as well as the performance characteristics of rapid HIV tests and proposed testing algorithms for diagnosing HIV infection.

The HIV Epidemic in the U.S.

Studies show that a substantial proportion of HIV-infected persons, approximately 40%, are diagnosed late in the course of infection and develop AIDS within a year of their HIV diagnosis. While the majority of AIDS cases are still concentrated among high-risk groups, such as blacks and men that have sex with men, the face of the epidemic is changing. Today, increasing numbers of cases are found in the following populations: individuals <20 years old, women, members of non-black racial minority groups, individuals who do not live in urban areas, and heterosexual men and women who believe they are not at high risk for contracting HIV.

Data from early CDC-sponsored HIV screening programs that were implemented in hospital emergency departments revealed a 2–7% positivity rate compared to 2% at STD clinics that tested high-risk individuals (1). This suggests that screening only high-risk individuals, although important, has limited success in identifying persons infected with HIV.

Overview of the CDC Guidelines

The 2006 CDC guidelines for HIV screening represented a shift from targeted screening of individuals at high risk or in high prevalence areas to routine screening of all individuals between the ages of 13–64 in all healthcare settings (1). Specifically, the recommendations allow for HIV screening under opt-out regulations, implying that consent to medical care and routine medical testing includes HIV testing. In addition, the guidelines recommend that individuals engaging in high-risk behavior should be screened at least annually. Similar provisions apply to pregnant women. CDC advises that routine prenatal screening include HIV testing and that repeat screening be performed in the third trimester in high HIV-prevalence populations.

Some Early Results

Although the release of the 2006 CDC guidelines offered the promise of widespread HIV screening, two years later, HIV screening is still limited and far from routine. Drawbacks include lack of funding for screening programs, limited ability to refer patients to subspecialty care, and laws in many states that prohibit opt-out testing. In fact, it would appear that few institutions have implemented the revised guidelines. A recent study revealed that only 57%, or 58 academic EDs surveyed, offer HIV screening with rapid tests. The majority of these offer HIV screening only for some special conditions such as occupational exposure (5).

Nevertheless, there are success stories from institutions that have made an effort to offer universal, opt-out HIV testing. One such example is the experience at George Washington University Medical Center (GWU) in Washington, D.C. (6). This academic institution offered HIV testing in accordance with the new CDC recommendations to patients being treated in the ED for a period of 3 months. During the study period, more than 4,000 patients were offered POC HIV screening and almost 2,500 (59.7%) accepted. There were 26 preliminary positives, of these 13 were lost to follow-up, 9 were confirmed positive and 4 were confirmed negative by Western blot. The authors estimated the cost at approximately $4,900 per confirmed positive case of HIV infection and concluded that routine, opt-out testing in EDs was cost-effective. The group also noted that they relied on the laboratory for QC and oversight of the POC testing and strongly encouraged other institutions to involve the laboratory in HIV screening programs.

A Look at Rapid HIV Tests

With the advent of rapid HIV tests, the options for screening have increased dramatically, as well as accessibility to screening and testing. In fact, many experts agree that expanded HIV screening would not be possible without rapid tests. These tests are now widely used in a variety of traditional and non-traditional healthcare settings, such as STD clinics, state health departments, community outreach programs, and labor and delivery settings (7). Furthermore, as hospitals around the country attempt to comply with CDC’s recommendations, rapid tests have become increasingly common in EDs (6, 8, 9).

Rapid HIV tests are screening tests, and therefore, any reactive result is considered a preliminary positive that must be confirmed with a Western blot or IFA for HIV-1 infection (10). While releasing preliminary HIV-positive results remains a concern, the potential benefits of increasing awareness of HIV status has resulted in widespread acceptance of this testing strategy.

Rapid HIV tests are extensively regulated in the U.S. and quite reliable. FDA insists that all rapid tests have >98% sensitivity and specificity for HIV infection. Currently, there are six FDA-approved rapid tests for HIV (Table 1, below). In general, the tests consist of single-use devices that cost approximately $20 and produce results in 30 minutes. Four of the FDA-approved rapid tests, OraQuick ADVANCE Rapid HIV-1/2 Antibody Test, Clearview HIV1/2 STAT-PAK, Clearview Complete HIV-1/2, and Multispot HIV-1/2 Rapid Test detect antibodies to both HIV-1 and HIV-2, but only the Multispot HIV-1/2 Rapid distinguishes HIV-1 from HIV-2 infection. Sample types include whole blood (fingerstick or venous), serum, plasma, and oral fluid. Four of the rapid tests use whole blood or oral fluid samples that do not need processing and are CLIA-waived. The remaining two tests, Multispot HIV-1/2 Rapid Test and Reveal G-3 Rapid HIV-1 Antibody Test, use plasma and serum exclusively and are therefore classified as moderately complex under CLIA and must be performed in a lab. Sensitivity ranges from 99.3% (OraQuick ADVANCE, oral fluid) to 100% (Multispot HIV-1/2 Rapid Test, serum and plasma and Uni-Gold Recombigen, serum and plasma). The specificity ranges from 98.6% (Reveal G3, plasma) to 100% (OraQuick ADVANCE Rapid HIV-1/2, whole blood) (Table 1, below) (11).

Table 1
FDA-Approved Rapid HIV Antibody Tests

Test

Manufacturer

Sample Type

Sensitivity

Specificity

OraQuick ADVANCE Rapid HIV-1/2 Antibody Test

OraSure Technologies
(Bethlehem, Pa.)

oral fluid

whole blood
(fingerstick or venipuncture)

plasma

99.3%

99.6%

99.6%

99.8%

100%

99.9%

Clearview COMPLETE HIV-1/2

Inverness Medical Professional Diagnostics
(Louisville, Colo.)

whole blood
(fingerstick or venipuncture)

serum and plasma

99.7%

99.7%

99.9%

99.9%

Clearview HIV-1/2 STAT-PAK

Inverness Medical Professional Diagnostics
(Waltham, Mass.)

whole blood
(fingerstick or venipuncture)

serum and plasma

99.7%

99.7%

99.9%

99.9%

Reveal G-3 Rapid HIV-1 Antibody Test

MedMira, Inc.
(Halifax, Nova Scotia)

serum

plasma

99.8%

99.8%

99.1%

98.6%

Uni-Gold Recombigen HIV

Trinity Biotech
(Berkley Heights, N.J.)

whole blood
(fingerstick or venipuncture)

serum and plasma

100%

100%

99.7%

99.8%

Multispot HIV-1/2 Rapid Test

Bio-Rad
(Redmond, Wash.)

serum

plasma

100%

100%

99.9%

99.9%

As these rapid tests have become more widely available, more information regarding their performance in different contexts has also become available. The overall performance of these assays is good; however, some problems have surfaced (12). For example, researchers determined that the specificity in their study population of the OraQuickADVANCE assay using oral fluid was 96.9%, in contrast to the manufacturer’s claim of 99.8% for this specimen type. Although these researchers found the use of rapid tests for HIV screening useful, with a reactive rapid test indicating an 8 to 32 fold increased odds of having HIV infection, they cautioned that specificity in real clinic settings may be lower than expected (8).

Episodic, unexplained increases in false-positive rates have also been observed with oral fluid samples. The original reports of increased rates of false-positive results occurred in 2005 at multiple sites including New York and Minnesota (13, 14). Although an investigation followed, a cause was never found (15). In late 2007, STD clinics operated by the New York City Department of Health and Mental Hygiene once again experienced an increased incidence of false-positive test results, prompting cessation of testing oral fluid samples (14). Unexplained clusters of false-positive results and lower-than-expected specificity with oral fluid samples in some clinical settings is a particular concern because this is the sample type preferred by both patients and testing staff. Moreover, oral fluid is the predominant sample type in many settings, including EDs.

Another concern is sensitivity of the tests. Although the sensitivity of the rapid tests is comparable with standard EIA tests, true sensitivity data may be somewhat limited in certain settings. For example, patients who test negative for HIV infection with a rapid test in EDs generally are not followed upon release from the hospital. In one study, a group of researchers evaluated four rapid tests for detecting acute infections: the OraQuick ADVANCE Rapid HIV-1/2, Clearview HIV-1/2 STAT-PAK, UniGold Recombigen HIV test, and the Multispot HIV-1/2 Rapid Test (16). The UniGold Recombigen appeared to be the most sensitive of all the tests studied, possibly because it is the only test that detects both IgG and IgM antibodies. In addition, the test requires a larger sample volume (50 µL) compared to the OraQuick and Clearview tests, which require only 5 µL of sample. Another possibility for the difference in sensitivities is inherent differences between kits and the different antigens used for antibody detection.

Although the exact cause of the UniGold Recombigen test’s increased sensitivity is not clear, overall the results indicate that the four rapid tests differ in their ability to detect acute infections. While this is not a surprising finding, it has important implications. Discordance between rapid tests, which actually represent acute HIV infection rather than negative serologic status, may impact recent proposals by some researchers to develop alternative testing algorithms composed solely of rapid tests for screening and confirmation.

Alternative Algorithms: No Western Blot?

Although rapid tests are strictly screening tests, recent proposals have suggested that two or more rapid tests or a combination of a rapid test and nucleic acid amplification test (NAAT) could be used in various testing algorithms to both screen and confirm HIV infection. One group of researchers evaluated 13 different assays that consisted of four rapid tests, at least one 1st, 2nd and 3rd generation EIA, and a variety of NAAT assays to address this issue (17). All tests were evaluated using a panel of known positive and negative samples for HIV infection and a seroconversion panel. Dual test algorithms using the tests in different combinations were either optimized for sensitivity or specificity. A three-test algorithm that used the results from the third test as a tiebreaker was also evaluated. The three-test algorithm provided the highest sensitivity and specificity, regardless of the test combination studied. Other findings of this study suggested that NAAT testing was most useful for acute infections, but less sensitive for long-standing HIV infection than antibody testing.

Compared to the traditional two-step EIA followed by Western blot confirmation, the researchers suggest that the alternative algorithms may cost less. In addition, they propose that these algorithms may be more feasible in outreach community programs. As an additional benefit, the alternative test algorithms do not appear to compromise sensitivity and specificity and may even reduce the ambiguity observed with indeterminate Western blot results. In fact, a San Francisco group recently developed and implemented a multiple, rapid HIV test algorithm (RTA) for distinguishing false, rapid-test results from true positives, using a three, rapid-test algorithm. The results suggest that such an algorithm can function and expedite referral for infected clients (18).

Other studies have focused on diagnosing acute HIV infections and have suggested algorithms that include rapid tests and NAAT (19, 20). The first FDA-approved NAAT for diagnosis and confirmation of HIV infection came on the market in 2006, the APTIMA HIV-1 RNA Qualitative Assay (Gen-Probe Incorporated, San Diego, Calif.).

Remaining Challenges

There is no doubt that the CDC guidelines have expanded and streamlined HIV testing using rapid tests. The expanded use of these tests in a variety of settings, both low and high risk, has provided critical information about their performance characteristics. These data are very useful for constructing new algorithms that may further decrease the time from screening to confirming HIV infection, with the ultimate goal of decreasing time to diagnosis and access to treatment.

In late 2007, CDC researchers, clinicians, and scientists met to evaluate the evidence for a number of alternative algorithms for screening and confirmation of long-standing and acute HIV infections. To date, no recommendations have been made. However, proposed alternative algorithms that rely heavily on the use of rapid tests and other technologies such as NAAT may someday replace the standard algorithm of EIA followed by Western blot that has been in place for the last 20 years.

Revised estimates of new HIV infection cases were published in 2008 based on results from a new antibody test, BED HIV-1 capture enzyme immunoassay, that can distinguish between long-standing and recent HIV infections (21). These data suggest that the previous estimate of 40,000 annual cases of HIV was an underestimate and that the real numbers may be as high as 56,000 cases annually, a 20% increase over previous estimates.

These figures reinforce the need to diagnose HIV-infected individuals and the rationale behind the CDC recommendations for universal HIV screening. More recently, CAP published a guidance statement that supports the CDC’s routine HIV screening recommendation (22). However, even the CDC admits that serious obstacles remain that prevent widespread implementation of the expanded HIV screening set forth in 2006. These include limited funding for HIV screening programs, controversy regarding the elimination of preventive counseling, and legal challenges to opt-out testing (23). Although progress is being made in tackling these obstacles, less than half of academic EDs expect to implement the CDC guidelines for routine HIV screening in the next 2–3 years (5).

In conclusion, HIV remains an important public health issue that continues to demand evolution of testing technologies and testing algorithms, as well as sustained funding and involvement of laboratorians.

References

  1. Branson BM, Handsfield HH, Lampe MA, Janssen RS, Taylor AW, Lyss SB, Clark JE. Revised recommendations for HIV testing of adults, adolescents, and pregnant women in health-care settings. MMWR 2006;55(RR-14):1–17.
  2. Ewings F, Bhaskaran K, McLean K, Hawkins D, Fisher M, Fidler S, et al. Survival following HIV infection of a cohort followed up from seroconversion in the UK. AIDS 2008;22:89–95.
  3. Marks G, Crepaz N, Janssen RS. Estimating sexual transmission of HIV from persons aware and unaware that they are infected with the virus in the USA. AIDS 2006;20:1447–50.
  4. Marks G, Crepaz N, Senterfitt J, Janssen R. Meta-analysis of high-risk sexual behavior in persons aware and unaware they are infected with HIV in the United States: implications for HIV prevention programs. J Acquir Immune Defic Syndr 2005;39:446–53.
  5. Ehrenkranz PD, Ahn CJ, Metlay JP, Camargo CA, Jr., Holmes WC, Rothman R. Availability of rapid human immunodeficiency virus testing in academic emergency departments. Acad Emerg Med 2008;15:144–50.
  6. Brown J, Shesser R, Simon G, Bahn M, Czarnogorski M, Kuo I, et al. Routine HIV screening in the emergency department using the new US Centers for Disease Control and Prevention Guidelines: results from a high-prevalence area. J Acquir Immune Defic Syndr 2007;46:395–401.
  7. Bulterys M, Jamieson DJ, O’Sullivan MJ, Cohen MH, Maupin R, Nesheim S, et al. Rapid HIV-1 testing during labor: a multicenter study. JAMA 2004;292:219–23.
  8. Walensky RP, Arbelaez C, Reichmann WM, Walls RM, Katz JN, Block BL, et al. Revising expectations from rapid HIV tests in the emergency department. Ann Intern Med 2008;149:153–60.
  9. Haukoos JS, Hopkins E, Eliopoulos VT, Byyny RL, Laperriere KA, Mendoza MX, Thrun MW. Development and implementation of a model to improve identification of patients infected with HIV using diagnostic rapid testing in the emergency department. Acad Emerg Med 2007;14:1149–57.
  10. CDC. Notice to readers: Protocols for confirmation of reactive rapid HIV tests. MMWR. 2004;53:221–2.
  11. CDC. General and laboratory considerations: rapid HIV tests currently available in the United States. US Department of Health and Human Services, 2007. Available at the CDC web site.
  12. Wesolowski LG, MacKellar DA, Facente SN, Dowling T, Ethridge SF, Zhu JH, Sullivan PS. Post-marketing surveillance of OraQuick whole blood and oral fluid rapid HIV testing. AIDS 2006;20:1661–6.
  13. Delaney KP, Branson BM, Uniyal A, Kerndt PR, Keenan PA, Jafa K, et al. Performance of an oral fluid rapid HIV-1/2 test: experience from four CDC studies. AIDS 2006;20:1655–60.
  14. CDC. False-Positive Oral fluid Rapid HIV Tests—New York City, 2005–2008. MMWR 2008;57:660–5.
  15. Jafa K, Patel P, Mackellar DA, Sullivan PS, Delaney KP, Sides TL, et al. Investigation of false positive results with an oral fluid rapid HIV-1/2 antibody test. PLoS ONE 2007.
  16. Louie B, Wong E, Klausner JD, Liska S, Hecht F, Dowling T, et al. Assessment of rapid tests for detection of human immunodeficiency virus-specific antibodies in recently infected individuals. J Clin Microbiol 2008;46:1494–7.
  17. Owen SM, Yang C, Spira T, Ou CY, Pau CP, Parekh BS, et al. Alternative algorithms for human immunodeficiency virus infection diagnosis using tests that are licensed in the United States. J Clin Microbiol 2008;46:1588–95.
  18. Knoble T, Delaney K, Menendez O, Dowling T, Facente S. Implementing a Multiple Rapid HIV Test Algorithm to Quickly identify False Positive Rapid tests and Provide Immediate Referral to Care for Persons Likely to be Infected with HIV, San Francisco, CA 2007. 2007. Available online.
  19. Pilcher CD, Fiscus SA, Nguyen TQ, Foust E, Wolf L, Williams D, et al. Detection of acute infections during HIV testing in North Carolina. N Engl J Med 2005;352:1873–83.
  20. Priddy F, Pilcher C, Moore R, Tambe P, Park M, Fiscus S, et al. Detection of acute HIV infections in an urban HIV counseling and testing population in the United States. J Acquir Immune Defic Syndr 2007;44:196–202.
  21. Hall IH, Ruiguang S, Rhodes P, Prejean J, An Q, Lee LM, et al. Estimation of HIV Incidence in the United States. JAMA 2008;300:520–529.
  22. Qaseem A, Snow V, Shekelle P, Hopkins R and Owens DK. Screening for HIV in Health Care Settings: A Guidance Statement From the American College of Physicians and HIV Medicine Association. Ann Inter Med 2009; 150(2): accessed before publication on December 12, 2008.
  23. Bartlett J, Branson B, Fenton K, Hauschild B, Miller V, Mayer K. Opt-Out Testing for Human Immunodeficiency Virus in the United States. JAMA 2008;300:945–51.

Patricia Slev, PhD, is assistant professor of path-ology (clinical) and medical director of Serologic Hepatitis and Retrovirus Laboratory at ARUP Laboratories, Salt Lake City, Utah.