However, in studies conducted in older adults, the elevated EPO production can potentially be triggered by an impaired oxygen delivery to the kidney, which can result from various pathophysiologic mechanisms such as anemia, hypoperfusion caused by renal arteriosclerosis, decreased renal blood flow or heart failure, decreased oxygen saturation due to diseases such as chronic obstructive pulmonary disease, and eryptosis-related decrease in blood oxygen capacity [18,39]. Here, EPO is linked to anemia (phenotype).