Blood Song (1982) 
A psychopath escapes from a mental asylum and goes on a killing rampage after having been locked up there for years as a consequence of witnessing his father kill his mother and then himself.
This development is offset by a young handicapped girl who is seeing visions of all the grisly murders taking place, which we later discover is due to her receiving a blood transfusion and therefore the killer's 'bad blood', which now courses through her veins and enables her to 'see' what he sees (at certain choice intervals of course).
So that handles the 'blood' element of the title. The 'song' aspect is covered by our psychopath's regular and eerily repetitive flute playing - a reminder of the father he barely knew who made it for him when he was a boy.
Overall Blood Song is a fairly effective little foray into psychosis and slasherdom, albeit silly and a little muddled in places.