We used our hrSMase-based assay to screen LDL aggregation susceptibility in samples derived from the Finnish Health 2000 Health Examination Survey,²⁰ which comprised largely healthy individuals (n = 100, Table 1, Figure 1B). To quantify the inter-individual variation in the aggregation susceptibility of LDL, we first developed a population-based generalized mixed-effect model (see Supplementary material online, Figure S3a). As described in the Supplementary material online, Methods, these data revealed that the inflection points in the curves of aggregate size vs. incubation time readily distinguished the aggregation susceptibility of the different LDL samples. Further, we found that LDL aggregate size at the 2-h time point correlated tightly and significantly with the inflection point (see Supplementary material online, Figure S3b, rho = −0.961, P < 0.001). Importantly, the extent of aggregation at 2 h clearly identified subjects having extremely aggregation-prone LDL particles (Figure 1C, Quartile 1). Therefore, in further assays, aggregate size at this time point was used as a measure of LDL aggregation susceptibility.