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Large US study shows which HIV tests are most accurate
Roger Pebody, 2014-01-06 08:50:00
Differences in the performance of commonly used HIV tests lead to substantial differences in the number of infections which are diagnosed in everyday clinical practice, according to an analysis from San Francisco published last month in PLOS ONE. If the test used only detects HIV antibodies, most acute (recent) HIV infections are missed, with the OraQuick rapid test also missing established infections when testing saliva samples.
However, a laboratory combination test – which can detect both antibodies and p24 antigen – has excellent performance, including in people who have acute infection. While a rapid combination test did not have as good results as the laboratory version, it was superior to rapid antibody tests.
In the first part of the study, clinicians re-examined the performance between 2003 and 2008 of a range of HIV tests used with high-prevalence San Francisco populations (sexual health clinics, a clinic for sex workers, people seeking PEP, people testing during contact tracing).
During this time in the city, antibody laboratory or rapid tests were supplemented with pooled testing of HIV RNA (i.e. a viral load test). This is considered the gold standard test for acute HIV infection – a person who tests negative on an antibody test but positive on HIV RNA is likely to have acquired HIV in the last few weeks. It is important to diagnose individuals who have acute infection as they have exceptionally high viral loads and contribute disproportionately to onward HIV transmission.
One aim of the study was to assess possible alternatives to the use of HIV RNA testing, as it is expensive and complicated to perform. For the second part of the study, the researchers therefore took stored samples of blood plasma of 58 people who had been diagnosed with acute infection and re-tested them using a wide range of tests, including fourth-generation ‘combination’ tests.
Across the 21,234 tests that had been performed, 761 people had been diagnosed with HIV (prevalence 3.6%), including 58 people with acute infection (prevalence 0.3%).
The main results are in the table. The key measures of accuracy are sensitivity (the percentage of results that are correctly positive when HIV is actually present) and specificity (the percentage of results that are correctly negative when HIV is not present).
As shown by the specificity scores of 99.9% or above, the study provides reassurance that false positive results are exceptionally rare – in other words, people who are HIV negative do correctly receive HIV-negative results.
Source:1
