The stats are a little old, but I don't imagine things differ much in 2022 from 2017.
Number 1 reason for blood donor deferral: low iron.
As mentioned in a previous post, I volunteered at 10 Red Cross blood drives in 2021. Based on what I've seen first-hand, yes, low iron levels are the biggest reason donors cannot give. Number 2 (far behind) would be blood pressure and/or heart rate (pulse) issues.
Other reasons for deferrals can be low body weight, high temperature, use of drugs (prescription or otherwise), and a "yes" answer to a wide variety of medical history questions.
Sometimes, I will see a donor get very frazzled/disturbed at being deferred. But, keeping the donor safe and keeping the blood supply safe are 2 of the highest priorities.
For low iron, pulse, blood pressure and temperature issues, the donor is only deferred for 24 hours anyway.
And Childrens Chewable Flintstone Vitamins work wonders (for many) at pumping iron levels up into the acceptable range.
Grace & Peace & Love to you all -
Matt