Home testing for HIV: Hopefully, a step forward
ABSTRACTAn over-the-counter at-home test for human immunodeficiency virus (HIV) infection has been approved and will likely be available soon. It is intended to decrease the percentage of HIV-infected people unaware of their infection (estimated at 18% of the 1.2 million people infected in the United States). Since early and continued treatment prevents disease progression and reduces HIV transmission, testing is the first step toward effective care.
KEY POINTS
- The new test is highly (99.9%) specific for HIV but is not quite as reliable at ruling out infection (93% sensitivity). Therefore, it may miss some cases of HIV, especially during the 90-day window after initial infection.
- False-positive test results may occur, especially in people at low risk. A positive result must be confirmed with a laboratory-based third- or fourth-generation blood test.
- It is important to continue to assess and counsel patients on how to modify their risk of HIV infection.
- Providers are urged to offer HIV testing to all patients ages 13 to 64 at least once, regardless of their risk.
- At least once a year, patients at high risk should get one of the more sensitive laboratory blood tests.
- People who choose to test themselves at home should seek medical care for verification of the test result and for HIV counseling, and, if the result is confirmed positive, access to HIV care.
LESS SENSITIVE THAN BLOOD TESTS
To provide additional care, clinicians must understand the performance of the home HIV test. Most importantly, the test result must be confirmed.
The In-Home test is less sensitive than currently available HIV blood tests used in the clinical setting, particularly the HIV-1/2 enzyme immunoassay (EIA) with confirmatory Western blot testing. The In-Home test is less likely to detect HIV infection during the 90-day “window period” when seroconversion is occurring, and so it should not be relied on to rule out HIV during this early period after infection.
The sensitivity and specificity of the OraQuick In-Home HIV test were determined in a phase III trial in 5,662 people (80% at risk of HIV), who were tested concurrently with the “gold standard” blood tests (EIA and Western blot). The sensitivity was 93% (giving a positive result in 106 of 114 patients who had a positive result on blood testing), and the specificity was 99.9% (giving a negative result in 5,384 of 5,385 patients who had a negative result on blood testing).7
Therefore, a positive In-Home test result is likely to be truly positive, but a negative result is not as reliably truly negative. False-negative results may occur particularly in the window period early after HIV infection, so the test should not be relied on within 90 days of high-risk behavior. In contrast, with the fourth-generation blood HIV tests, the window period is approximately 16 days.
The predictive value of the test will depend on the population using it and on the patient’s pretest probability of disease at the time of testing. In the population tested by OraQuick, the positive predictive value was 99.1% and the negative predictive value was 99.9%.7 Mathematical modeling has been done to examine the potential outcomes for use in subpopulations at lower risk and at higher risk.
As clinicians, we will have to address the potential for both false-positive and false-negative test results. False-positive results may be more likely in low-risk populations and may occur in the setting of cross-reactive antibodies from pregnancy, autoimmune diseases, or previous receipt of an experimental HIV vaccination. False-negative results may occur in the setting of acute HIV infection and in those with severely impaired immunity (eg, from agammaglobulinemia or immunosuppressive drugs) and will be more likely in higher-risk populations, such as men who have sex with men, intravenous drug users, blacks, and Hispanics ages 18 to 35 with multiple sexual partners. A positive In-Home HIV test should be followed up with a blood EIA and confirmed with Western blot in all patients.
WHO WILL USE THIS TEST?
It is unclear who will use this new test. In OraSure’s clinical trial, the percentages of people who indicated they would “definitely or probably buy” the test were:
- 20% of the general population
- 27% of those ages 18 to 35
- 49% of blacks ages 18 to 35
- 47% of homosexual men
- 43% of people who said they had more than two sexual partners per year
- 32% who said they use condoms inconsistently.
If this is true, the test may appropriately target several populations that are not currently being tested, either because they lack access to care or because they do not see themselves as being at high risk. Of those with newly diagnosed HIV infection from 2006 to 2009, 40% had had no prior testing, and the groups with the highest percentages of people in this category were black, men with injection drug use as their sole risk factor, those older than 50 years, and those with heterosexual contact as their sole risk factor.8 Because of difficulties in identifying some of these groups as “at risk,” the current CDC guidelines recommend that HIV testing be offered to all patients ages 13 to 64, regardless of their risk factors.9
The home HIV test may fill a gap in testing, extending it to those still not tested in the health care setting or to those who have not sought health care. For the home test to fill that gap, people still have to perceive themselves as at risk and then purchase the test. Through public health strategies and at clinical points of care, we must continue to inform our patients about HIV risk and work to identify new or ongoing risk factors that would prompt additional testing.
MANY QUESTIONS REMAIN
- Will those who need testing want to use this test? People will buy the test only if they perceive themselves to be at risk.
- Is this test affordable for the target populations? $60 will be unaffordable to some.
- Will the directions be followed effectively?
- Will home testing reduce opportunities to counsel patients on their HIV risk factors?
- Will there be situations in which individuals are socially pressured to take the test?
- Can users of the test expect the appropriate amount of privacy? Availability on the Internet and in drug stores is not a guarantee of privacy when purchasing the test, although the result presumably will not be known.
- Will those with positive results seek medical care?
- Will those with negative results who are still at high risk forgo more sensitive testing and continue to engage in high-risk activities?
Nevertheless, since early and continued treatment prevents disease progression and reduces HIV transmission, testing is the first step toward access to effective HIV care. The home HIV test is a step forward in providing high-quality HIV testing to the wider population.
