A blood donor might be deferred for any of several reasons: recent illness; exceeding permitted levels of prescribed medications; hypoglycaemia; pregnancy; too young/too old; underweight (you have to have sufficient blood volume to make a full donation); recent tattooing; and various other criteria, including the previously-mentioned male-to-male sexual contact and risk factors for Creutzfeldt-Jakob disease (i.e. having been treated with human growth hormone, or residence in the UK during specified period). The triage nurse, having assessed your statement of disclosure, may allow your donation to go ahead. However, all blood taken is tested, and only some components of it may be used.