The APTIMA assay, which detects the RNA--the nucleic acid or genetic material--of the HIV-1 virus, is the first test approved for the detection of HIV-1 RNA to help diagnose HIV-1 infection. HIV-1 is the main virus that causes AIDS.

"This product offers medical diagnostic laboratories the ability to perform a gene-based test for HIV-1 that, until now, was only available as part of a larger kit used to screen blood and plasma donors," said Jay Epstein, M.D., director, Office of Blood Research and Review, Center for Biologics Evaluation and Research (CBER), FDA. "This test also can detect infection with HIV-1 earlier than HIV antibody tests when used to detect primary HIV-1 infection."

This test has important implications for medical diagnostic use because it could be a potential alternative to the traditional Western blot test now used for confirmation of HIV-1 infection when screening tests for HIV-1 antibodies are positive. In addition, the Western blot can, in some instances, be difficult to interpret and may not always provide a conclusive result. In such cases, the APTIMA test may be helpful in HIV-1 diagnosis. The APTIMA test can also be used in clinical laboratories and public health facilities to detect early HIV-1 infection, before the appearance of antibodies to HIV-1.

The sensitivity of the APTIMA assay is comparable to that of FDA approved viral load assays that measure the amount of HIV-1 virus circulating in the blood of patients with established HIV-1 infection to monitor the treatment and progression of AIDS. Unlike the viral load tests, the APTIMA test has been approved for the diagnosis of primary HIV-1 infection, as well as for confirming HIV-1 infection when tests for antibodies to HIV-1 are positive.

CBER, one of six centers within FDA, is responsible for the regulation of biologically-derived products, including blood intended for transfusion, blood components and derivatives, vaccines and allergenic extracts, and cell, tissue and gene therapy products. CBER also regulates AIDS-related diagnostic tests.

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The researchers note that the relationship between DNA length and emission wavelength agreed with calculated values based on well-established theoretical models, with the ruler displaying an average wavelength shift of 1.24 nanometers per base pair cleaved. The investigators also comment that because this method can detect changes in plasmon light emission from single gold nanoparticles, it should be useful in microfluidics-based high-throughput screening assays aimed at identifying proteins or drugs that alter DNA structure.

This work, which was supported in part by the National Cancer Institute, is detailed in a paper titled, A nanoplasmonic molecular ruler for measuring nuclease activity and DNA footprinting. Investigators from the University of California at Berkeley, the University of New Mexico Health Sciences Center, and the University of California at Riverside also participated in this study. An abstract of this paper is available at the journal ™s website. View abstract.

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