This is why you get an iron test when you give blood and the necessary threshold is set above what counts as anemic - you can faint while giving even if your iron is only slightly down. It's also one of the reasons why the nice folks at the donation center tell you not to do any...
Cardiovascular: Low blood pressure (resulting in dizziness, light-headedness or fainting when getting up from a lying, sitting or squatting position) and irregular heartbeat. polyclinic.singhealth.com.sg 心血管系统:低血压(导致坐起或站起时感到昏眩、头晕或 昏 厥) 、心 率失调 polyclinic.singheal...
Vavic N, Pagliariccio A, Bulajic M, Dinić R, Marinozzi M. Giving blood donors something to drink before donation can prevent fainting symptoms: is there a physiological or psychological reason? Transfusion and Apheresis Science. 2014;51:65-9....