2015). This suggests that NT‐proBNP is not a pure marker of volemia, but rather likely reflects eGFR, modification of heart structure in addition to volemia. In a similar manner, we attempted to determine whether arterial stiffness could be used as a tool to hint toward changes in RBCV. However, in contrast with our previous studies in healthy young volunteers where arterial stiffness is related to anemia and may decrease Hb production by regulating Epo production, arterial stiffness did not correlate with blood volumes in the current study (Montero et al. 2016). Here, EPO is linked to anemia (phenotype).