A new diagnostic technique has been developed which allows for the diagnosis of HIV within less than one week of infection. The new tool makes possible the detection of HIV viral load as low as two copies/ml, considerably lower than the limit of detection available with the RNA PCR tests currently used to measure viral load. The development of these improved testing methods is reported in the July edition of the American Journal of Clinical Pathology, which is now available on-line.
Known as Real-Time Immuno-PCR, the new testing methods were developed by investigators at the Institute of Human Virology, at the University of Maryland in Baltimore. It allows for the earlier detection of HIV by looking for an inner protein of HIV called p24, rather than antibodies to HIV or HIV's nucleic acid. Each particle of HIV contains 3,000 molecules of p24 compared to only two of RNA which means that there is a greater target for the test to detect.
“It’s an advance over current methods” of testing, said investigator Dr Janet Barletta, “we can now detect down to the equivalent of two copies of RNA as compared with the current methods which have been validated to only 50 copies.”
Using the new test clinicians will also be able to detect the presence of HIV infection earlier. The earliest that current testing technologies can detect HIV infection is twelve days after exposure, but the Baltimore investigators showed that the Real-Time Immuno-PCR could be used to diagnose HIV less than a week after infection. This would allow not only earlier diagnosis of HIV, but also enhance protection of the blood supply.
The Real-Time Immuno-PCR has the ability to more sensitively detect levels of HIV and “has the potential to become the most sensitive method available for the determination of HIV-1 infection by determination of the presence of HIV-1 p24 antigen at an earlier time than is attainable by any serologic or molecular method presently in use”, conclude the investigators.
The new test is not yet commercially available and is therefore not yet available in clinics. Before this happens, the Real-Time Immuno-PCR needs to be validated in clinical trials both as a predictor of disease progression and treatment response.
Further information on this website
Monitoring treatment with viral load - overview
Undetectable viral load - overview
Testing during primary infection - overview
Barletta JM et al. Lowering the detection limits of HIV-1 viral load using Real-Time Immuno-PCR for HIV-1 p24 antigen. American Journal of Clinical Pathology 122 (on-line edition), 2004.