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14:195-207. to all or any four laboratories. Using SBA titers from the tilt method for all samples, and using MC HPA as the comparator, the results were as follows for NZ ESR, NIPH, and Chiron, respectively, using log10 titers: correlation coefficients (= 0.89, slope = 0.833, and intercept = ?0.05 when the log10 titer of the second run was regressed on the log10 titer of the first run. Additionally, complement is known to be added in excess to the reaction mixture, even when the test sera are Finafloxacin hydrochloride heat inactivated. NZ ESR and MC HPA retested the study sera only once more, using serum complement bridged to the plasma supplied by NIPH, which introduced an added variable to the testing procedure. Chiron did not implement changes, and its original data set was used for the repeat analysis. Statistical analysis. MC HPA, NZ ESR, and NIPH used a starting dilution in the SBA assay of 1 1:2, while Chiron commenced with a dilution of 1 1:4. For the analyses presented here, samples with Finafloxacin hydrochloride recorded titers below 4 were set to a titer of Finafloxacin hydrochloride 2 for statistical analyses. For all analyses, within-subject-visit geometric means were used as the titers for NIPH (two assay runs) and Chiron (three assay runs), and single measurement determinations were used as the titers for HPA and NZ ESR. Thus, for the repeat study, the variances associated with the subject-blood draw data are theoretically different among the four laboratories. As a result, the differences in the number of replicate measurements between labs have an effect on the precision of the reported titers and thus on the comparison of results FN1 between labs. All data manipulation and statistical analyses were conducted using SAS for Windows version 9.1.3. Pearson’s chi-square test was used to determine whether the proportions of fourfold increases in SBA between the different laboratories were significantly different. This chi-square test does not account for the paired nature of the data (in that each of the four laboratories was testing the same subject samples). To account for the paired nature of the data, an analysis of variance (ANOVA) model was used to test whether the mean = 21), post-first dose (= 21), post-second dose (= 20), and post-third dose (= 16) sera. Prevaccination and post-third-dose vaccination data were available for all laboratories for 15 of the 21 subjects. Table ?Table11 shows that the percentages of subjects with SBA titers of 4 were discrepant between laboratories in the initial study across all four blood draws (with the exception of post-first and post-third dose data between NZ ESR and NIPH). TABLE 1. Percentages of subjects from initial study with SBA titers of 4 by time of blood draw and laboratory = 0.753 for chi-square test). An additional ANOVA, tested in a model that accounted for subject, showed that the average increase in titer (within a subject) from prevaccination to post-third-dose vaccination did vary from laboratory to laboratory (= 0.0213). SBA GMTs with 95% CIs are shown in Table ?Table4.4. SBA GMTs between MC HPA and NZ ESR, NIPH, and Chiron each were compared separately for prevaccination, post-first dose, post-second dose, and post-third dose samples in an ANOVA model. For post-third dose samples, Chiron’s GMTs were higher (at a 5% level of significance) than the MC HPA GMTs. No other significant differences were found (Table ?(Table55). TABLE 4. SBA GMTs with 95% CIs per time of blood Finafloxacin hydrochloride draw for each laboratory value for lab effect on GMT)= 76) between NZ ESR and MC HPA.