Rapid oral HIV screening tests: In low prevalence settings, reactive tests need confirmation

In 2006, the Centers for Disease Control and Prevention (CDC) recommended that all adults be offered an HIV screening test in healthcare settings throughout the United States.  Since then, more than 150 emergency departments across the country have been expanding HIV screening efforts.  Such public health interventions are possible because new technologies allow rapid HIV tests to be conducted on either blood or oral fluid samples and provide patients with results within 20 minutes.

In a new study, researchers at Brigham and Women’s Hospital (BWH) have found that one of the most commonly used rapid HIV tests, when conducted on oral fluid in a low prevalence emergency department population, may lead to a high rate of false positive results.  In this study, researchers report that out of 849 adults tested with the oral rapid HIV test, 31 persons had reactive results. Five patients were truly HIV-infected upon confirmation.  84 percent of positive rapid screening tests turned out to be false when further testing documented that the patient did not have HIV infection.  These findings are published in the August 5, 2008 issue of the Annals of Internal Medicine.

“The rapid test is still useful to screen to patients for HIV infection.  Patients with a reactive test had up to 32-fold increased odds of having HIV infection compared to their pre-test odds.  We have learned that a reactive test does not mean that the patient is HIV-infected but rather that confirmation is required,” said Rochelle Walensky, MD, MPH lead author on the paper and an Infectious Disease physician at BWH.

The researchers found that in every 100 patients tested in the emergency department, 95 leave knowing that they are HIV-negative, and five patients leave with confirmation pending.  One in these five is typically identified as actually having HIV.

Christian Arbelaez, MD, MPH, a BWH emergency physician and study co-author, noted “We continue to use this test in our study at the BWH Emergency Department because we recognise that every screening test has trade-offs. The advantages of the oral, rapid test are that it is easy to use, acceptable to patients and has correctly identified cases of HIV infection that we would have otherwise missed.”

With HIV screening efforts growing throughout the United States, the timing of these results is critical.  This study underscores the importance of proper management of results from HIV screening tests conducted in emergency departments and elsewhere.  Patients should understand before testing that reactive (positive) results are only preliminary.  Furthermore, providers should be readily equipped to handle reactive results, which often occur in the absence of true disease, and there must be a well-defined mechanism for confirmatory studies and follow-up.

“It is critical to provide a balanced interpretation of the results of our study,” commented Elena Losina, PhD, senior author of the report. “We cannot simply blame the test; we need to recognise that even tests with excellent performance characteristics will lead to false positive results in low prevalence settings.  The most important message from our study should focus on proper management of patients with reactive rapid HIV test results given increased number of persons being tested for HIV in the US.” 

“We must consider the performance of this test in the context of other large-scale screening programs, such as mammogram screening for breast cancer.  When we screen for disease, false positive results are expected, especially if the disease is uncommon. ‘Positive’ results of any screening test require definitive confirmation.  At a new HIV-case identification rate of 0.6%, I am satisfied that we have successfully used the OraQuick® test to identify patients who might have been overlooked,” said Walensky.

(Source: Annals of Internal Medicine: Brigham and Women’s Hospital: August 2008)