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 cl inical trials. Thus, variability in these measurements may significantly af fect their interpretation in clinical practice and research. The variabilit y in consecutive measurements of plasma HIV RNA levels was studied in 387 s ubjects receiving either stable nucleoside reverse transcriptase inhibitor therapy or no treatment. The Pearson's correlation coefficient between base line measures 2 weeks apart was 0.92. The mean SD in consecutive measuremen ts 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 consecut ive measures 1 month apart was due to biologic fluctuation; one-third was d ue to assay variance. The biologic variance increased proportionately with the number of weeks between assessments. Clinicians and investigators shoul d be aware of the magnitude of variability in viral RNA levels in the HIV-i nfected population.