Ten laboratories requested PPP specimens for analyses with SELDI chip fractionation, MS analysis, and algorithm-based differentiation of m/z peaks across specimens. Rai et al.  report the cross-laboratory evaluation of eight submitted datasets, of which five were judged appropriate for comparison of plasma results and four for serum results. Intra-laboratory CV varied from 15 to 43%. Correlations across labs were 0.7 or higher for 37 of 42 spectra with signal/noise ratios >5. More detailed analyses were done to actually identify one protein, haptoglobin, and variation in the intensity/concentration of its subunits in the different PPP reference specimens. They recommend stringent standardization and pre-fractionation to increase the usefulness of this method.
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