Longitudinal Variability of Human Immunodeficiency Virus Type 1 RNA Viral Load Measurements by Nucleic Acid Sequence-Based Amplification and NucliSens Assays in a Large Multicenter Study

Human immunodeficiency virus type 1 (HIV-1) RNA measurements were evaluated within an externally controlled multilaboratory program. Three external standards (1.5 × 10(3) to 1.5 × 10(6) copies/ml) were included in 814 assay runs by four laboratories. Results indicate that HIV-1 RNA levels can be measured with a precision equal to that of the pre-highly active antiretroviral therapy era (standard deviations, ±0.16 to 0.25 log(10) units).