How much iron is removed per donation

Each unit of whole blood contains approximately 200 to 250 milligrams of iron, mostly bound within haemoglobin in the red blood cells. This is a meaningful quantity: the total iron stores of an average adult are roughly 3,000 to 4,000 milligrams, so a single donation removes around 6 to 8 percent of total body iron.

For a healthy adult eating a varied diet containing both haem iron from meat and non-haem iron from plant sources, this amount is replenished within four to eight weeks through normal dietary absorption. The body also increases the efficiency of iron absorption from food in the weeks following donation, partly compensating for the loss through a hormonal mechanism involving hepcidin.

Hereditary haemochromatosis and therapeutic donation

Hereditary haemochromatosis is the most common genetic condition in people of Northern European descent. It causes the body to absorb far more iron from food than it needs, leading to progressive accumulation of iron in the liver, heart, pancreas, joints and other organs. If untreated, this iron overload causes liver cirrhosis, diabetes, heart disease and joint damage.

The standard treatment for haemochromatosis is venesection, the therapeutic removal of blood, which is mechanically identical to blood donation. In many cases, people with haemochromatosis are able to donate through NHS Blood and Transplant rather than through a purely clinical venesection pathway, meaning their therapeutic need is met simultaneously with a life-saving donation. The donated blood from people with haemochromatosis is safe for transfusion in most circumstances.

How the body regulates iron after donation

When iron stores fall after donation, the body responds through several mechanisms. Hepcidin, a hormone produced by the liver that regulates iron absorption, decreases in concentration. Lower hepcidin levels signal to the gut to absorb more iron from food. Erythropoietin, a hormone produced by the kidneys, increases to stimulate the bone marrow to produce more red blood cells.

This feedback system means healthy donors who eat a varied diet recover their iron stores reliably between donations at the standard intervals. The 12-week interval for men and 16-week interval for women are calibrated to give this recovery system enough time to operate effectively before the next donation.

Iron overload beyond haemochromatosis

Hereditary haemochromatosis is the most common cause of iron overload but not the only one. Secondary iron overload can occur in people who receive multiple blood transfusions, those with certain anaemias that increase iron absorption, and in some liver conditions. For people in these groups, therapeutic phlebotomy or regular donation may similarly help manage elevated iron levels under medical supervision.

If you suspect you have elevated iron levels for any reason, the appropriate first step is a blood test through your GP to measure serum ferritin and transferrin saturation, not self-directed blood donation. Donation is not a substitute for diagnosis and medical management of iron overload.

The risk at the other end: donation and iron depletion

While iron overload donors clearly benefit from the iron-reducing effect of donation, healthy donors who give blood at the maximum frequency face the opposite risk: cumulative iron depletion over time. This is particularly relevant for menstruating women, vegetarians and vegans, and anyone with a diet low in iron-rich foods.

The pre-donation haemoglobin check provides a safety net by deferring donors whose haemoglobin has fallen below the minimum threshold. But haemoglobin can be within range while ferritin, the stored form of iron, is already low. Donors who donate frequently and experience persistent fatigue, breathlessness or repeated near-deferrals should ask their GP for a ferritin test.