Is it sinful to expose part of the arm in front of a non-mahram man for blood donation, and does that affect the acceptance of good deeds?

Donating blood is among the virtuous deeds when there is a need, but it is not obligatory. It is not permissible for a woman to expose her arm to a non-mahram man or for him to touch her for the purpose of donation, except in cases of necessity that make the donation incumbent upon her.