Estimation of measurement error in plasma HIV-1 RNA assays near their limit of quantification.
BACKGROUND
Plasma HIV-1 RNA levels (pVLs), routinely used for clinical management, are influenced by measurement error (ME) due to physiologic and assay variation.


OBJECTIVE
To assess the ME of the COBAS HIV-1 Ampliprep AMPLICOR MONITOR ultrasensitive assay version 1.5 and the COBAS Ampliprep Taqman HIV-1 assay versions 1.0 and 2.0 close to their lower limit of detection. Secondly to examine whether there was any evidence that pVL measurements closest to the lower limit of quantification, where clinical decisions are made, were susceptible to a higher degree of random noise than the remaining range.


METHODS
We analysed longitudinal pVL of treatment-naïve patients from British Columbia, Canada, during their first six months on treatment, for time periods when each assay was uniquely available: Period 1 (Amplicor): 08/03/2000-01/02/2008; Period 2 (Taqman v1.0): 07/01/2010-07/03/2012; Period 3 (Taqman v2.0): 08/03/2012-30/06/2014. ME was estimated via generalized additive mixed effects models, adjusting for several clinical and demographic variables and follow-up time.


RESULTS
The ME associated with each assay was approximately 0.5 log10 copies/mL. The number of pVL measurements, at a given pVL value, was not randomly distributed; values ≤250 copies/mL were strongly systematically overrepresented in all assays, with the prevalence decreasing monotonically as the pVL increased. Model residuals for pVL ≤250 copies/mL were approximately three times higher than that for the higher range, and pVL measurements in this range could not be modelled effectively due to considerable random noise of the data.


CONCLUSIONS
Although the ME was stable across assays, there is substantial increase in random noise in measuring pVL close to the lower level of detection. These findings have important clinical significance, especially in the range where key clinical decisions are made. Thus, pVL values ≤250 copies/mL should not be taken as the "truth" and repeat pVL measurement is encouraged to confirm viral suppression.
British Columbia Centre for Excellence in HIV/AIDS, Vancouver, British Columbia, Canada.|Division of AIDS, Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.
Viviane D
http://orcid.org/0000-0003-4943-091X
VD
Lima
British Columbia Centre for Excellence in HIV/AIDS, Vancouver, British Columbia, Canada.
Lu
L
Wang
British Columbia Centre for Excellence in HIV/AIDS, Vancouver, British Columbia, Canada.
Chanson
C
Brumme
Statistics Department, University of British Columbia, Vancouver, British Columbia, Canada.
Lang
L
Wu
British Columbia Centre for Excellence in HIV/AIDS, Vancouver, British Columbia, Canada.|Division of AIDS, Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.
Julio S G
JS
Montaner
British Columbia Centre for Excellence in HIV/AIDS, Vancouver, British Columbia, Canada.|Division of AIDS, Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.
P Richard
PR
Harrigan
D000328:Adult; D019380:Anti-HIV Agents / Q000627:therapeutic use; D018791:CD4 Lymphocyte Count; D005260:Female; D015658:HIV Infections / Q000097:blood / Q000188:drug therapy / Q000821:virology*; D015497:HIV-1 / Q000235:genetics* / Q000302:isolation & purification*; D006801:Humans; D057230:Limit of Detection; D008297:Male; D008875:Middle Aged; D012367:RNA, Viral / Q000097:blood* / Q000235:genetics*; D019562:Viral Load / Q000379:methods* / Q000706:statistics & numerical data
D019380:Anti-HIV Agents; D012367:RNA, Viral