Biomedical Engineering Reference
In-Depth Information
Fig. 12 ANA-BA stability at
higher temperatures. Stability
of ANA-BA at 40 C was
between 100 and 110% in
comparison with ANA-BA
stored at 4 C
120%
100%
80%
60%
40%
20%
0%
PosC
dsDNA
Ro60
Ro52
La/SSB RNP/Sm
Scl-70
Table 2 Analysis of analytical performance of ANA-BA
Ro60 Ro52 Scl-70 dsDNA CENP-B Sm RNP/Sm La/SS-B
Specificity (%) 96 96 96 96 100 100 100 97
Sensitivity (%) 94 91 63 74 90 100 100 95
Kappa 0.903 0.879 0.668 0.678 0.920 0.943 0.986 0.910
All values determined for negative control (NegC) population were omitted from calculations of
means. PosC, positive control
ANA-BA shows a dynamic measurement range over at least three log10 steps.
Intra-assay precision mostly does not exceed 5%, a value achieved by most
common ELISA for antibody detection [
40
]. It seems that some antigens like Ro60
generally show a reduced precision, perhaps because it is more difficult to protect
their immune reactive epitopes during the manufacturing process and storage.
Inter-assay precision was found to be below 12%. This general finding for inter-
assay precision is similar to other microbead-based assays [
38
,
41
] or diagnostic
biochips [
37
] and seems to be sufficient in semi quantitative testing. Kappa values
of ANA-BA are comparable with standard ELISA and are in most cases ''very
good'' (see below). However, inter-assay precision below 10% would be desired if
quantitative antibody detection is the aim. Interestingly, the inter-assay CV of the
anti-dsDNA antibody detection is 4.8%, the only parameter that requires quanti-
fication to increase the ANA-BA's clinical value [
42
]. In contrast, inter-batch
precision with a mean over all parameters of 10.2% is, as expected, higher than
intra- and inter-assay precision, since the batches applied in this study were
manufactured during the not fully standardized final product development process.
Comparison of ANA-BA with reference ELISA provided relative sensitivities
of C 63%, and relative specificities of 100%, which is in good agreement with the
findings of Wagner et al. [
43
]. Because considerable conflicts between ELISA and
microbead assay results have been described [
38
,
44
-
46
], it is important to
mention that the degree of accordance between most of the reference ELISA
and ANA-BA is kappa C 0.8 and therefore ''very good''. The high specificity of
ANA-BA is underlined by the findings that none of the blood donor sera showed
any specific AAB activity, which is in accordance with the low AAB prevalence in
the healthy population [
42
].
