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Novel Approaches to HIV Antibody Testing

New methods of HIV antibody testing are available that promise to change how patients and clinicians view the testing process. Several of these tests -- home tests, rapid tests, and non-serum tests -- are already FDA approved, and more are likely to be approved soon.

HIV Antibody Testing: Current Status

As currently practiced, HIV antibody testing consists of a screening ELISA and confirmatory Western blot. Practically, this two-test approach requires two visits. Optimally, at the first visit, pretest counseling is given and informed consent is obtained; blood is sent to a laboratory, and patients return in one to two weeks for test results and post-test counseling. At its best, post-test counseling offers support and a plan of action for those who test HIV positive, as well as encouraging behavioral change in those who test negative. Additionally, the theory of the "window period" and the need for repeat testing at a later date for recent exposures are explained.

Accuracy of this testing method is excellent. Specificity (likelihood that a person without infection will have a negative test) is greater than 99.9%.^1,2 Because of the "window period" of negative antibody after acute infection that averages about 4 weeks, sensitivity (likelihood that person with infection will have a positive test) depends on the incidence of new infections in the community. In low-prevalence populations such as blood donors, it is also greater than 99.9%.³

However, despite this high test performance, there are several drawbacks to testing as currently performed. Although only 24 hours are required to complete the ELISA/Western blot testing algorithm, most labs batch specimens for processing, causing a one-to-two-week wait for definitive results. One study has shown that 40% of those tested never returned for their test results.^4,5 Perhaps because of concern about maintaining anonymity or other factors, many individuals with HIV are not tested until they develop symptoms. Up to one third of patients receive their HIV diagnosis within two months of progression to AIDS.⁶ Another drawback of today's testing practice is that pre- and post-test counseling frequently do not meet published standards.⁴

Cost and the time investment of the two-step process have also impeded testing. Even when tested without charge at a publicly-funded clinic, clients must take time out of work or caring for children for waiting time, counseling, and travel. The true cost of this process has been estimated at $41 per test.⁴ Individuals tested in private offices may incur not only the cost of the test by commercial or hospital labs, but also the physician's office fee.

Home Test Collection Systems

Companies have been interested in developing kits for home HIV testing since the FDA approved the first HIV antibody test for serum in 1985. Initially, opposition was encountered from the FDA, the CDC, and AIDS advocacy groups.⁷ People were concerned whether notification of test results by telephone or mail was as safe as traditional face-to-face notification. Public health officials worried that surveillance programs could not monitor home-HIV testing results. One major safety concern has been a theoretical increased risk of suicide in those testing HIV positive, and the adequacy of phone support. However, it is not clear that this increased risk actually exists.^8,9

View this table: [in a new window]   Table 1. Summary Information on Available Tests

 

It also remained unclear if home testing would actually lead to wider testing of populations at risk. In the 1992 National Health Interview Survey, 22% of all respondents and 31% of those with one or more risk factors for HIV infection stated that they would choose a home test over other testing modalities. Those more likely to choose home testing were male, less than 44 years old, of lower educational or socioeconomic status, or those with perceived risks for HIV.¹⁰ Others have favored home testing because of convenience.¹¹ A further benefit is anonymity.

Confide

On May 14, 1996, the FDA approved the first HIV home-test kit. This system is called Confide and is manufactured by Direct Access Diagnostics, a subsidiary of Johnson & Johnson. Confide is an over-the-counter specimen-collection kit; the testing is done by central laboratories.^7,12

The Confide kit includes a pretest counseling booklet, a 14-digit randomly-generated personal identification number, and blood-sampling materials. The purchaser uses a retractable lancet to prick a fingertip and place a few drops of blood on a filter paper test card.¹³ The sample is sent to the medical laboratory in a prepaid, pre-addressed protective mailer; no personal information is required.

At the lab, the sample is tested by HIV-1 enzyme immunoassay (EIA). Positive EIAs are repeated twice. If a repeat EIA is also positive, the sample is tested by Western blot or IFA. A specimen of adequate quantity and quality is crucial to ensuring an accurate result.

HIV-antibody activity in dried blood extracts has been proven comparable in test performance to ELISA and Western blot of serum.¹⁴ Confide was tested in clinical trials on three populations -- known HIV-infected individuals, those at high risk for HIV infection, and blood donors. One hundred percent of 150 known HIV-positive persons were correctly identified as seropositive by Confide testing. Negative samples were correctly identified 99.95% of the time on evaluation of over 3940 known negative samples.¹²

Results are available in seven days. If the result is negative, the listener hears a recording of the result when calling the information line. He or she is given the option to speak with a live counselor or to access other recorded information. If the result is positive, indeterminate, or not tested, the listener is referred to a counselor. Seropositive persons may call back for unlimited counseling over a two-year period. Counselors help to develop an action plan and provide names of approved AIDS treatment centers in the appropriate geographic area. (Dr. G. Noble, personal communication.)

The Confide home collection system can be obtained by calling 1-800-THE-TEST. Test kits are delivered by Federal Express for $49.95 plus tax. Kits are also available over the counter at major pharmacies for $35-40.

Home Access

The other HIV home-collection kit on the market is the Home Access HIV-1 Test System, which was FDA approved on July 22, 1996. This product is manufactured by Home Access Health Corporation (HAHC).

As with Confide, blood-spot specimens are collected by pricking a fingertip with a provided lancet. A filter paper circle must be completely filled with blood and allowed to dry. At the lab, samples are eluted and tested by EIA. All samples repeatedly positive on at least two of three EIAs undergo HIV-1 IFA. If the sample is negative on initial testing or if it is EIA positive and IFA negative, the sample is reported as negative.¹⁵

The Home Access System was tested in a four-center study of subjects at high risk for HIV infection. Of the 756 subjects, 164 (22%) were found to be HIV-1 positive by routine serum testing. Of those positives, 150 subjects also provided samples adequate for home testing. All 150 known seropositive individuals were correctly identified by the Home Access System, for a sensitivity of 100% (95% CI, 99.7-100%). The test kit was also studied at five centers with HIV prevalence similar to the U.S. population. Four hundred and seventy-one subjects found to be seronegative by the home collection kit had matching venous results, for a specificity of 100% (95% CI, 99.6-100%).¹⁵

The quality of Home Access blood-spot specimens obtained by untrained users have also been analyzed. In the clinical trials, 9.6% of users had at least one problem with specimen collection; most commonly the need for more than two fingersticks to obtain an adequate blood specimen. Despite this, most were able to provide an adequate blood spot. Ninety-three percent of specimens received at the lab were judged adequate in quantity and quality for testing.¹⁵

During the clinical trials, only one to two percent of participants reported adverse events including dizziness, anxiety, ecchymoses, and syncope, none considered serious.¹⁵

Results of Home Access testing are available by telephone within 3 to 7 days. Participants with negative results and those who submitted an insufficient sample may retrieve their results directly from the interactive voice response system and also have the option to speak with a counselor. Unlike the Confide test, the Home Access test refers a predetermined percentage of persons with negative results to a counselor to deter callers from assuming such referral implies a positive result. All persons with positive or indeterminate results are referred immediately to a counselor, who reports results and offers referrals to clinics and physicians, information on partner notification services, and numbers for the National AIDS Hotline. Individuals with indeterminate results are also offered a new kit to be used in six to twelve weeks, or referred to outside sites for traditional HIV testing. Negative results are available for 30 days after the first call and positive results are available on-line for up to one year. Positive results are archived and available thereafter from the medical director.¹⁵

The Home Access System may be obtained by calling 1-800-HIV-TEST or from some pharmacies. Home Access travels by U.S. mail, takes 7 days to obtain results, and costs $44.95 by phone order and $39.95 at local pharmacies. Home Access Express travels by Federal Express, takes 3 days to obtain results, and costs $54.95 by phone order and $49.95 in pharmacies. (HAHC, personal communication.)

Confide and Home Access are beginning postmarketing studies to verify safety and efficacy under conditions of routine use. Additionally, they plan to assess utilization rates, entry into health care delivery systems, and acceptance of results by health care professionals. (Dr. G. Noble and HAHC, personal communication.)

True Home Testing

As noted above, neither Confide nor Home Access is a true home test, since users must send their specimens in for testing. A true home-test kit contains all pre- and post-test counseling information and sample collection materials. The user purchases the test at pharmacies or by mail order, performs it at home, and has a result within several minutes.

True home testing for HIV infection is anonymous, low cost, and accessible, potentially improving the chances for earlier diagnosis. However, the ramifications of receiving such information at home are unknown.¹¹ It remains unclear whether persons identified as HIV positive will enter the health care system and how public health officials could maintain surveillance. Another potential disadvantage is that individuals who test HIV negative may not get counseling about risk modification.⁴

Opponents of true home-HIV testing are concerned about potential for abuse. Parents might force children to be tested but not be prepared to deal with a positive result.¹⁶ Sex partners, employers, insurance companies, and immigration officials may use undue pressure to persuade an individual to be tested. Such nonclinical uses raise concerns about domestic violence and other forms of abuse.^4,10,11 Without a telephone counselor, true home-HIV testing demands a level of understanding by the test taker -- including the need for confirmation of a positive test and the meaning of a negative test in the window period.¹¹ Since companies will be seeking licensure for true home-HIV tests soon, studies are needed on the outcomes of home testing and standards for its use need to be defined.

Rapid HIV Testing

Rapid HIV assays are those that yield results in 30 minutes or less. Potential advantages include elimination of the need for a return visit and the ability to take action immediately in acute situations such as blood and organ donation, pregnant women with unknown HIV status presenting for labor, and occupational exposure.^5,16,17

The only rapid assay currently licensed by the FDA is the Single-Use Diagnostic System (SUDS) HIV-1 test from the Murex Corporation. This assay utilizes EIA and is recommended by the company as an initial screening test. (Murex, personal communication.) Negative results need no further testing, but positive results must be confirmed by Western blot or IFA.

The SUDS assay has been validated for use in STD and HIV clinics. In a CDC study, all 39 specimens that were positive by EIA and Western blot were correctly identified by the SUDS test, yielding a sensitivity of 100% (95% CI, 88.8-100%). Of the negative specimens, seven were positive on SUDS test with a specificity of 99.5% (95% CI, 98.9 to 99.7%). The authors found that the SUDS test was affected by elevated temperature and centrifugation.¹⁸ As part of a test of six rapid HIV-1 assays, the SUDS test had a sensitivity of 100% and a specificity for known seronegative samples of 99.5%. However, specificity dropped to 91.8% for sera that were indeterminate by Western blot.¹⁹ This test may not be suitable for screening populations with a large proportion of recent seroconverters who may be indeterminate on Western blot. Performance of the rapid HIV assay depends on both the competence of the person performing the test and the proper handling of all reagents. (Dr. W. Kassler, personal communication.)

The current SUDS test was licensed by the FDA in 1992. Murex reports sensitivity at 99.9% and specificity at 99.6%. List price is approximately $9 per test but controls must be purchased separately. A 30-test kit is also available for $283, encouraging batch testing to lower cost. Results of the assay are available within 10 minutes. (Murex, personal communication.)

As noted above, studies have demonstrated that rapid HIV testing can be performed with sensitivity comparable to conventional testing methods but lower specificity. Practically, this means the test can safely be used to rule out HIV infection, and patients with negative results can be informed that they do not have HIV. The lower test specificity, however, makes the false-positive rate unacceptably high. It should not be used to make a definitive diagnosis of HIV infection. The positive predictive value (likelihood that the positive test is a true positive) will be particularly low in low-prevalence populations such as blood donors and sources of occupational exposure. As a result, positive rapid tests should more accurately be labeled "inconclusive," with follow-up standard HIV testing performed to confirm or rule out HIV infection.⁴ Knowledge of inconclusive serostatus on the day of testing may promote early behavior modification and encourage individuals to return for confirmatory testing.^4,17,20

Non-Serum-Based HIV Testing

Novel HIV tests of saliva or urine rather than blood, are being marketed. These offer several advantages over conventional serum tests, including needleless sample collection, easier waste disposal, and minimal training of personnel. Oral fluid and urine testing appeal to people unable or unwilling to undergo blood sampling, including intravenous drug users and children.¹¹

Oral Fluid HIV Testing

Oral fluids include whole saliva collected by dribbling or spitting, pure saliva (salivary gland secretions), and gingival crevicular fluid, an oral mucosal transudate (OMT). OMT has the highest levels of salivary IgG, only 1/800th of those in serum, but stable and reproducible over time.²¹ Dental status has not been shown to affect detection of viral antibodies in OMT.²²

OraSure, an FDA-approved oral specimen collection device, was licensed in May 1996. OraSure is marketed by Epitope, Inc. and has clinical support from the SmithKline Beecham Laboratories. The OraSure HIV-1 collection device is not intended for home use and specimens may be collected only by health care workers. The device consists of a cotton pad impregnated with salts and gelatin and attached to a nylon stick. The pad and its contents create a hypertonic environment to encourage transudation of OMT across mucosal surfaces. The pad is rubbed between the lower gum and cheek until moistened and left in place for two to five minutes. On removal, the pad is placed in a solution containing antibiotics and preservative enzymes and sent to the central laboratory by routine mail. Specimens remain stable at room temperature for up to 21 days.²³

At the laboratory, the OraSure specimen is processed by EIA (Oral Fluid Vironostika HIV-1 Microelisa System). Negative EIA results are reported as negative while positive results are repeated by EIA. Specimens that are repeatedly positive on EIA testing undergo OraSure HIV-1 Western blot. Results of Western blot are positive, negative, or indeterminate, as for serum samples.²³

Clinical trials of the OraSure HIV-1 testing algorithm were performed on low-risk, high-risk, and known HIV-positive populations. OMT results were compared with serum Western blot. The OraSure EIA correctly identified 241 of 242 known seropositive subjects as HIV positive. However, only 236 of these specimens were positive by OraSure Western blot and six were indeterminate. One EIA result was falsely negative but no OraSure Western blot false negatives were found. The OraSure system was also evaluated on 2897 seronegative subjects. The combination of oral fluid EIA and Western blot correctly identified 2893 of 2897 specimens as negative, giving a specificity of 99.9%.²³ In a field study of the OraSure test, one out of 195 subjects developed new buccal ulcers one day after testing.²⁴

OraSure HIV-1 tests may be obtained only at physician offices, clinics, and hospitals, which may obtain OraSure collection kits by calling 1-888-ORASURE, ext. 302. Three test kits are sold for $99 and results are available by phone or fax within three days of mailing. (OraSure, personal communication.)

Urine HIV testing

On August 6, 1996, the FDA approved the first urine HIV test.^25-29 It was created by the Calypte Biomedical Corporation³⁰ and is marketed by Seradyn, Inc. as the Sentinel HIV-1 Urine EIA. The test is a rapid IgG capture EIA utilizing a recombinant envelope protein of HIV-1 to detect HIV-1 antibodies in urine. Specimens that are negative on EIA are reported as such. Specimens that are EIA positive are repeated in duplicate in a manner similar to serum EIA algorithms. If the EIA is repeatedly reactive, the patient has confirmatory serum testing. To date, there is no urine Western blot, although data have been presented to the FDA Blood Advisory Committee.⁴ (Calypte, personal communication.)

The sensitivity and specificity of the Sentinel HIV-1 Urine EIA are less than for serum; it is currently marketed for public health and clinic screening. It is not recommended for screening of blood donors because it is less sensitive and specific than blood testing. Sentinel test kits are available to professional laboratories through Seradyn, Inc. (1-800-428-4007). Sentinel HIV-1 Urine EIA is run on 12x8 microwell plates. Up to 90 specimens, including controls, can be run in each batch at a cost of about $4 per well. The assay is sold in a 192-test kit for $816 or a 480-test kit for $1920. (G. Albrecht, personal communication.)

Conclusions

Many of the described testing approaches offer clear technical advances over the traditional two-step ELISA/Western blot (or other confirmatory test) done on serum. These newer tests are potentially more convenient and less invasive, have shorter turnaround times and, in the case of home testing, are more user-controlled. By some analyses, they would even be cost-effective -- the savings accrued by using a rapid HIV antibody test after an occupational exposure would likely be substantial. Based on studies done prior to licensing, many of the tests have acceptable and in some cases excellent sensitivity and specificity.

Despite these advantages, several questions remain. How accurately will they perform in "real world" settings? How will the poor pay for testing not covered by insurance or government programs? How effective is counseling offered over the phone or by printed material? What criteria will the companies use to choose sites for referral for HIV care? If the rapid tests become more widely used, how will we communicate to patients the results of a reactive test? (This would be analogous to reporting a positive ELISA to a patient prior to receiving the results of the Western blot.) When approved, how will true home testing -- where the user obtains the result -- be monitored to avoid abuses? How will public health departments track infection rates?

A recent patient experience illustrates some of these dilemmas. Knowing he was at risk for HIV infection, this patient chose to be tested using an approved home-test kit to avoid encountering someone he knew at an anonymous test site and taking time out from work. He found the educational material enclosed to be clear and the instructions for use easy to understand; he submitted the specimen for testing. However, when he called for his results after a week, he was told there were technical problems with his test, and he should call back in one week. One week later, he was informed by a live counselor that his test was positive. He was given the phone number of a nearby center for HIV care, but when he called, he was told that this clinic was no longer accepting new patients. Ironically, he received his referral for health care by asking advice from an anonymous test site.

Despite such problems, this patient preferred the home test and has no regrets.

His experience illustrates two contrary aspects of these new tests. First, there will be significant challenges to providing error-free testing and counseling services, especially early in these tests' implementation. Second, there will be a subset of individuals who prefer these methods of testing to approaches offered so far. Only through systematic study of these tests after their marketing will we be able to draw definitive conclusions about the appropriateness of their use and their impact on HIV care.

Dr. Sax is an associate editor of ACC; Dr. Brodie is an infectious disease fellow at the Brigham and Women's Hospital. Neither has interest or investment in the tests or manufacturers discussed in this article.

— Sharon Brodie, MD, and Paul Sax, MD

Published in AIDS Clinical Care January 1, 1997

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