In order to do this, researchers from the University of California, San Francisco (UCSF) conducted a review of over 21,000 HIV tests performed between the years 2003 and 2008 in some of the city’s high-prevalence populations.
Of four types of tests used during this period—from first-generation antibody tests to rapid oral tests—761 people were diagnosed with HIV (3.6% prevalence), while 58 were identified during acute infection.
The study also aimed to compare the accuracy of newer testing assays—including fourth-generation antigen/antibody tests—by retesting the blood from the 58 people previously diagnosed with acute HIV infection.
As accuracy is related to sensitivity (the percentage of tests that were positive in a person with the condition) and specificity (the percentage of tests that were negative in a person without the condition), the take-home message is that there is room for improvement in HIV testing to capture more acute infection.
By contrast, the rate of false negatives varied considerably, with the saliva-based OraQuick Advance rapid test performing the worst, with just over 1 in 15 people receiving a false negative result.
The figure only worsened when retesting bloods from the acute stage infections. Of the 58 samples tested, the third-generation rapid tests achieved a sensitivity of only 5.2% to 25.9%, meaning that the majority of such infections would be missed using these rapid, antibody-based tests.
Even the fourth-generation Determine rapid antigen/antibody test was able to identify only half of the acute infections, despite having an estimated sensitivity of 96.6% and specificity of 100%. According to the UCSF researchers, the Determine test worked best during acute infection when the patient’s viral load was over 500,000.
Making an Informed Choice
In terms of testing selection and performance, the following conclusions can be reasonably drawn:
Commercial, over-the-counter HIV tests perform the least well overall, not only in terms of detecting acute infection but in returning a false negative rate of 7%. Combination HIV antigen/antibody tests are far more accurate than traditional antibody-based assays, particularly during the acute stage of infection. Lab-based tests still outperform at-site, point-of-care HIV tests, most especially in cases of recent HIV exposure.
With that being said, high levels of sensitivity are only part of the reason why certain tests are preferred over others.
For example, a significant number of people fail to return for their results after testing. The ability to return a result within 20- to 30 minutes makes rapid testing the ideal choice for most people (and increases the likelihood that they’ll be linked to care).
Similarly, people with confidentiality concerns or fears about HIV stigma may be better served by taking an in-home rapid test. While there remains little data as to the number of people linked to care following a positive result, it is presumed that the tests will at least provide an entry point for those who might otherwise avoid testing clinics.
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