OPG likely shows sensitivity to the distribution of RA patients based on the sTfR-F index, as it tends to increase in the ACD subgroup (p = 0.053) compared to the combined anemia subgroup, as shown in Figure 1, but there is no significant difference in OPG levels between the subgroups based on Hb levels. Here, TNFRSF11B is linked to anemia (phenotype).