Just so you know, CBS tests hemoglobin not iron (I always thought that was an iron test too). On their information page about hemoglobin and iron, they state that someone can have normal hemoglobin but low iron. Actually, from what I've read since this happened to me, it seems that simply testing hemoglobin is insufficient to know if your iron levels are good.

A recent study of 550 Canadian donors (500 with normal hemoglobin & 50 with low) was performed and some of its findings included:

• More than a third of first-time female donors and about two thirds of repeat female donors had low or absent iron stores.
• Iron stores were rarely low in first-time male donors, but were low in more than a third of repeat donors.
• Hemoglobin levels and ferritin levels did correlate somewhat; donors who failed or just passed the hemoglobin test (“low pass”) had lower ferritin levels than donors with a “high pass” (130 g/L or greater).

The findings were summarized:

Blood donors selflessly provide the gift of life, and Canadain Blood Services owes it to them to minimize any ill-effects on their health. In Canada, a dedicated group of repeat donors provide close to 90% of the donations we receive. We are incredibly grateful for such generous donors, who return time and again to give. This study showed that a significant proportion of our whole blood donors are iron deficient and that iron deficiency relates strongly to sex and frequency of donation.

Apparently CBS is now starting to measure iron (ferritin) in some locations, but I think this is still in trials.

A larger US study (2,425 donors) was also done a couple years ago and it found:

Among frequent donors, two-thirds (66%) of the women and almost half (49%) of the men were iron deficient. The true prevalence of iron deficiency among regular donors is surely higher; the RISE study enrolled only frequent donors who had been accepted for donation, excluding those deferred for a low hemoglobin concentration ... Neither these loyal donors nor the national blood supply are well served by the collection practices and regulatory framework that have produced widespread iron deficiency among those who regularly give their blood.

Again, this is not to say that donation is bad or that everyone who donates is going to become anemic. However, it is prevelant enough that I think it's wise for regular donors to meet with their doctors, test their iron (ferritin) levels, and come up with a plan for donation and monitoring that ensures they are not compromising their health while donating. Unfortunately, I do not think the cursory tests performed by the agencies that collect donations are sufficient to ensure a donor's good health.