INTERLABORATORY AGREEMENT AMONG RESULTS OF HUMAN PAPILLOMAVIRUS TYPE-16 ENZYME-LINKED IMMUNOSORBENT ASSAYS

Serological assays for measuring antibodies to human papillomavirus ty pe 16 (HPV-16) virus-like particles (VLPs) have become important epide miologic tools in recent years, However, the interlaboratory replicabi lity of these assays has not been assessed, In this investigation, thr ee laboratories tested a panel of specimens obtained from two differen t groups: 265 subjects in a vulvar cancer case-control study and 107 h ealthy volunteer blood donors. Each laboratory used an enzyme-linked i mmunosorbent assay (ELISA), but no attempt was made to standardize ass ay procedures among the three laboratories. The data showed good day-t o-day intralaboratory replicability in laboratory 1 (correlation coeff icient, greater than or equal to 0.88) and good intra-assay variabilit y in laboratory 3 (correlation coefficient, greater than or equal to 0 .93). Interlaboratory correlations, likewise, ranged between 0.61 and 0.80 in both case-control study subjects and healthy blood donors, ind icating that ELISA optical density (OD) values between laboratories we re linearly related regardless of the population, Kappa coefficients ( kappa), based on each laboratory's categorical interpretation of its r esults (as positive or negative), showed good agreement (kappa, > 0.6) in case-control study subjects and moderate agreement (kappa, greater than or equal to 0.4)in blood donors, a population that had few stron gly positive sera, When OD values near seropositive cutoffs were treat ed as indeterminates, there was little discordance between laboratorie s in either population, The data suggest that each laboratory measured the same humoral immune response and that their HPV-16 VLP ELISAs per formed similarly (Pearson correlations). Interlaboratory differences, however, probably due to reagents and procedures, were considerably gr eater than intralaboratory day-to-day variability, Interlaboratory agr eement in determining seropositivity (kappa) could be improved by shar ing positive and negative serum controls and by treating marginal resu lts as indeterminate. As part of continuing cooperation to improve int erlaboratory agreement, we are preparing bulk serum control specimens to be shared and made available to interested researchers.