Blood is definitely a motif in Macbeth. The metaphorical/symbolic meaning of blood throughout the play is somewhat up to interpretation. I would say that there are a few things you could argue about this.

For example; blood could be considered an outward manifestation of the inward guilt felt by the Macbeths. The conversation that Lady Macbeth and Macbeth have after Duncan's murder is a good indicator of this. Lady Macbeth talks about washing the blood away by saying "a little water clears us of this deed". This shows that she does not feel the guilt of the murder at this time. Macbeth, on the other hand, believes that instead of water washing the blood off his hands, his hands could turn an entire ocean red with blood.

Your interpretation of the significance of blood can be defended with many quotes. I've linked below to Shakespeare navigator, which shows quotes from the play containing the word "blood".