As shown in Supplemental Table 1, according to CFS, CCI, and CFS, patients in Cluster 1 were non-frail with low levels of BNP (i.e., Cluster 4 in k-means), Cluster 2 low BNP pre-frail to frail, pre-frail-to frail (k-means Cluster 2), Cluster 3 high BNP, pre-frail-to frail (k-means Cluster 3), Cluster 4 very frail patients with high BNP (k-means Cluster 1). Here, NPPB is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.