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Journal of Clinical Microbiology, 07 1997, 1751-1756, Vol 35, No. 7
HD Strickler, A Hildesheim, RP Viscidi, KV Shah, B Goebel, J Drummond, D Waters, Y Sun, NL Hubbert, S Wacholder, LA Brinton, CL Han, PC Nasca, R McClimens, K Turk, V Devairakkam, S Leitman, C Martin and JT Schiller
Serological assays for measuring antibodies to human papillomavirus type 16
(HPV-16) virus-like particles (VLPs) have become important epidemiologic
tools in recent years. However, the interlaboratory replicability of these
assays has not been assessed. In this investigation, three laboratories
tested a panel of specimens obtained from two different groups: 265
subjects in a vulvar cancer case-control study and 107 healthy volunteer
blood donors. Each laboratory used an enzyme-linked immunosorbent assay
(ELISA), but no attempt was made to standardize assay procedures among the
three laboratories. The data showed good day-to-day intralaboratory
replicability in laboratory 1 (correlation coefficient, > or = 0.88) and
good intra-assay variability in laboratory 3 (correlation coefficient, >
or = 0.93). Interlaboratory correlations, likewise, ranged between 0.61 and
0.80 in both case- control study subjects and healthy blood donors,
indicating that ELISA optical density (OD) values between laboratories were
linearly related regardless of the population. Kappa coefficients (kappa),
based on each laboratory's categorical interpretation of its results (as
positive or negative), showed good agreement (kappa, > 0.6) in
case-control study subjects and moderate agreement (kappa, > or = 0.4)
in blood donors, a population that had few strongly positive sera. When OD
values near seropositive cutoffs were treated as indeterminates, there was
little discordance between laboratories in either population. The data
suggest that each laboratory measured the same humoral immune response and
that their HPV-16 VLP ELISAs performed similarly (Pearson correlations).
Interlaboratory differences, however, probably due to reagents and
procedures, were considerably greater than intralaboratory day-to-day
variability. Interlaboratory agreement in determining seropositivity
(kappa) could be improved by sharing positive and negative serum controls
and by treating marginal results as indeterminate. As part of continuing
cooperation to improve interlaboratory agreement, we are preparing bulk
serum control specimens to be shared and made available to interested
researchers.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
Interlaboratory agreement among results of human papillomavirus type 16 enzyme-linked immunosorbent assays
National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
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