It often arises from reduced iron intake, impaired intestinal absorption, gastrointestinal bleeding (e.g., by concomitant use of aspirin), uraemia (e.g., CKD), venepuncture, chronic low-grade inflammation or inhibition of EPO synthesis (CKD, possible due to use of angiotensin-converting inhibitors (ACE-I) or angiotensin receptor blockers (ARB)) [41, 42]. Here, EPO is linked to chronic kidney disease.