While high correlation between the distinct assays suggests specificity, for proteins with weaker correlation or those that do not overlap between the platforms, we leveraged WGS **data** to help further inform each reagent's specificity. If a protein's measure by a given platform is associated with genetic variation near the cognate gene (i.e., cis pQTLs), this supports the protein assay's accuracy. WGS was available in 489 of the JHS participants, and a validated computational pipeline for variant-protein association analysismatching that previously described for pQTL identification-was used in the present analysis (21). Many of the proteins for which cis pQTLs were identified in the present analysis also have cis pQTLs that were previously identified in the literature in populations with predominantly European ancestry: 425 target proteins have previously known cis pQTLs, although these were not necessarily specific to Olink or Soma1.3K (table S2). Conversely, we identified previously unknown cis pQTLs for 373 protein targets by this method. Cis pQTLs could be identified for 595 of 1472 (40%) of the reagents on the Olink platform and 370 of 1301 (28%) of reagents on the Soma1.3K platform at a P < 1 × 10 −5 (table S2). At this threshold, 164 of the reagent pairs show a cis pQTL for both reagents. If a genome-wide significance threshold is used (5 × 10 −8 ), cis pQTLs are observed for 368 of 1472 (25%) Olink reagents and 206 of 1301 (16%) Soma1.3K reagents. At this threshold, 98 reagent pairs have cis pQTLs for both reagents. Figure 3B shows the presence of pQTLs on either platform for matched reagents, relative to their correlation. While highly correlated reagents were both likely to demonstrate a cis pQTL, proteins with a lower correlation were more likely to show a cis pQTL for the Olink reagent only (Table 1).