Why must a donor weigh at least 50 kilos?

The minimum weight requirement is based on blood volyme.

The human body contains approximately five litres of blood. For safety reasons, the blood extracted for a donation, which totals around half a litre, may not exceed 10% of the total blood in the body.

The amount of blood in the body depends on your body weight, and for those weighing under 50 kg it is so small that donating increases the risk of post-donation complications such as faintness, nausea or dizziness.

The same weight limit is given in many international recommendations and is mentioned in the European Blood Directive, with which all Member States must comply.​