Variability in repeated consecutive measurements of plasma human immunodeficiency virus RNA in persons receiving stable nucleoside reverse transcriptase inhibitor therapy or no treatment

Plasma human immunodeficiency virus (HIV) RNA levels correlate closely with clinical prognosis in both treated and untreated HIV-infected persons and are widely used to guide clinical practice and as a primary end point in clinical trials. Thus, variability in these measurements may significantly affect their interpretation in clinical practice and research. The variability in consecutive measurements of plasma HIV RNA levels was studied in 387 subjects receiving either stable nucleoside reverse transcriptase inhibitor therapy or no treatment. The Pearson's correlation coefficient between baseline measures 2 weeks apart was 0.92. The mean SD in consecutive measurements 1 month apart was 0.31 log(10) copies/mL with a 95% tolerance limit of 0.7 log(10) copies/mL (5-fold). Two-thirds of the total variance in consecutive measures 1 month apart was due to biologic fluctuation; one-third was due to assay variance. The biologic variance increased proportionately with the number of weeks between assessments. Clinicians and investigators should be aware of the magnitude of variability in viral RNA levels in the HIV-infected population.