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Hi Alfa,
You can use smartprofile module for adding blood type field and you can make it as required field during the registration, or you can hack the current profile and replace for example ICQ with Blood type .. I need time for make this hack .. it is too easy.
Regarding to donors module .. you can use xroster module after modify some lang files to be blood donation module, example:
http://ljr-lab.ruc.dk/xoops/modules/xroster/