Check for problems with oral rapid HIV tests
If your clinic is using oral fluid samples for rapid HIV testing, be sure to monitor for false-positive results. Between October 2007 and April 2008, the New York City Department of Health and Mental Hygiene documented a higher-than-usual percentage of false-positive oral HIV tests in its sexually transmitted disease (STD) clinics, with the false-positive rate reaching 1.1% in some months.1
While this rate is below the Food and Drug Administration (FDA) threshold of 2%, it is higher than expected.
In January 2004, the STD clinics introduced on-site rapid HIV testing of finger-stick whole-blood specimens using the OraQuick brand test (OraSure Technologies; Bethlehem, PA). In March 2005, the clinics replaced finger-stick whole-blood testing with oral fluid testing with the OraQuick Advance Rapid HIV-1/2 Antibody Test.
On average, during January 2004-February 2005, less than one false-positive finger-stick whole-blood rapid test occurred monthly. In October 2005, after the switch was made to oral samples, clinicians noticed an increase in the number of false-positive test results each month. From an average of five false-positive tests per month, the monthly number of false-positive tests increased to 11 (0.27% of 4,024 tests) in October 2005 and to 36 (0.97% of 3,735 tests) in November 2005. In late December 2005, a revised strategy was implemented whereby clinics continued to offer oral fluid rapid tests but immediately followed reactive oral fluid tests with a second OraQuick test on finger-stick whole-blood specimens. By February 2006, an oral fluid test specificity of 99.65% was observed, within the confidence interval of manufacturer's specifications.
Another persistent increase
Clinicians recorded another persistent increase in false-positive oral fluid test results in late 2007. Beginning in November 2007, the number of false-positive oral fluid tests increased from 23 (0.51% of 4,503 tests) to a peak of 54 (1.11% of 4,858 tests) in February 2008. During November 2007-April 2008, the monthly specificity of the oral fluid test ranged from 98.88-99.49%. In May 2008, fewer false-positive tests occurred; in that month, five (0.11% of 4,749 oral fluid tests) were found to be false-positive (specificity: 99.89%).1
The city's STD clinics have switched to rapid blood tests while investigating the problem, says Susan Blank, MD, MPH, assistant commissioner of the department's Bureau of Sexually Transmitted Disease Control. While the reason for the slight increase in false-positive tests is not clear, the health department is working with the Centers for Disease Control and Prevention (CDC) and the manufacturer to identify the cause. At this point, the false-positive tests have not been linked to test kit handling, storage conditions, lot numbers, clinic sites, or test operators, the department reports.
The CDC will continue to monitor for problems with HIV testing to minimize possible adverse events associated with inaccurate test results, says Bernard Branson, MD, associate director for laboratory diagnostics in the Division of HIV/AIDS Prevention at CDC. The agency has not received additional verified reports of increases in false- positive test results, he notes. It is encouraging testing programs to let the CDC and the manufacturer know if they experience elevated levels of false-positive test results in their area.
CDC consistently recommends that all rapid test programs monitor confirmatory test results after reactive rapid tests and report any unexpected events to the manufacturer and CDC, Branson advises. Confirmatory HIV testing remains an essential part of establishing an accurate diagnosis of HIV, he explains.
Positive results from rapid tests are considered preliminary, and according to CDC recommendations, should be followed up with an FDA-approved confirmatory test before a diagnosis of HIV is given to the patient. If this procedure is followed, any false-positive rapid test results will be resolved promptly, Branson notes. (Editor's note: To review all CDC guidance on rapid HIV testing, go to the CDC HIV/AIDS web center, www.cdc.gov/hiv. Under "Topics," click on "testing." Under "HIV Testing," click on "Rapid HIV Testing" to access a broad spectrum of information, including test comparison charts, training information, and laboratory specifications.)
Rapid tests effective
When it comes to HIV testing, rapid HIV antibody tests offer public health officials new opportunities to improve access to testing in clinical and nonclinical settings and increase the number of people who learn their results.
Such an approach to testing has been effective, research indicates. During September 2003 through December 2005, the CDC purchased and distributed rapid HIV tests in one effort to expand testing and assess the feasibility of using rapid tests in new environments, such as outreach settings or emergency departments. In an analysis of that effort, in which the CDC distributed tests to 230 organizations, clinicians identified 4,650 (1.2%) HIV infections among 372,960 rapid tests administered.2
"Rapid tests, including oral fluid rapid tests, remain a critical part of efforts to reduce HIV infections in the United States," says Branson. "Patients are substantially more likely to receive their test results when tested with rapid vs. conventional HIV tests, and many patients prefer noninvasive oral fluid testing."
Reducing obstacles to HIV testing is an important part of CDC's strategy to reach the more than 250,000 Americans estimated to be living with HIV who are not aware of their infection, Branson states. These individuals may be unknowingly transmitting the virus to their partners and are unaware of their need for treatment, he notes.
"Far too many Americans with HIV are diagnosed late in their infection — nearly 40% within a year of developing AIDS,3" says Branson. "Testing is an essential first step in linking people with HIV to effective medical care and ongoing support to help them maintain safer behaviors."
Focus stays on testing
Rapid testing is an important part of New York City's public health response to the HIV epidemic; the Health Department provided close to 60,000 HIV rapid oral tests in 2007, which is twice the number it administered in 2003.4 Blank estimates some 6,000 tests were performed in June 2008.
The switch to whole-blood rapid tests has not proven to be a problem for patients or clinicians, says Blank. It did not affect the city's participation in National HIV Testing Day. In fact, the city rolled out its "Bronx Knows" public health push to help all Bronx borough adult residents know their HIV status within the next three years.
Bronx residents account for nearly one-fourth of New York City's HIV infections and one-third of the city's AIDS deaths each year.5 Among Bronx residents who tested positive in 2006, more than 25% already were sick with AIDS by the time they learned they had HIV.5
"Every day for us is National HIV Testing Day. That is really the case," says Blank. "Our HIV testing numbers continue to increase."
References
- Centers for Disease Control and Prevention (CDC). False-positive oral fluid rapid HIV tests — New York City, 2005-2008. MMWR 2008; 57:660-665.
- Centers for Disease Control and Prevention (CDC). Rapid HIV test distribution — United States, 2003-2005. MMWR 2006; 55:673-676.
- Neal JJ, Fleming PL. Frequency and predictors of late HIV diagnosis in the United States, 1994 through 1999. Presented at the Ninth Conference on Retroviruses and Opportunistic Infections. Seattle; February 2002.
- New York City Department of Health and Mental Hygiene. Health department statement regarding rapid HIV testing. Press release. June 22, 2008.
- New York City Department of Health and Mental Hygiene. Health department launches Bronx-wide HIV testing initiative. Press release. June 26, 2008.
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