Board Thread:General Discussion/@comment-4317207-20130327210703/@comment-11051098-20130807140109

Quincy Zangetsu said to Ichigo when he was revealed to he Ichigo's Quincy powers, that he used Blut Vene a few times before on his own initiative to help him. I think one of those times were indicated to be stopping the massive bleeding from a wound Ichigo got from Kenpachi in their first fight.

I think that's why Ichigo appeared to be able to use Blut Vene, and that to a skilled extent, without ever having been trained.