DETECTION OF LOW HIV-1 RNA LEVELS IN PLASMA

HIV-1 viremia is a marker of choice for staging, prognosis, and monito ring treatment efficiency in HIV infection. Among the commercial assay s, the Amplicor HIV Monitor (Roche, Basel, Switzerland) test has the h ighest sensitivity for HIV-1 RNA quantitation in plasma with a detecti on limit of 200 copies per milliliter. To measure HIV-1 viremia below this threshold, boosted versions of the Amplicor assay were developed by adding a centrifugation step prior to RNA extraction and by decreas ing dilution factors. In the boosted version, the increase in analytic al sensitivity for HIV-1 RNA detection directly correlates with the in put of plasma. For 1,500 mu l of plasma, the sensitivity of the assay increases by a factor of 30. For routine clinical analysis, we use a b oosted assay format with an input plasma volume of 500 mu l and a lowe r detection limit of 20 copies/milliliter. Coefficients of intra- and interassay variation are similar to those reported for the standard as say (similar to 30%). Thirteen (45%) of 29 plasma samples of HIV-infec ted individuals with undetectable viremia in the standard assay had de tectable viremia between 20 and 200 copies/milliliter.