Blood arrives in dreams already sacred. The Hebrew scriptures state the principle outright, that the life of the flesh is in the blood, which is why blood belonged to the altar and not to the table, and cultures far beyond Israel have treated it as the substance in which life itself is carried, spilled in sacrifice, sworn in covenant, feared in taboo. A dream interpreter inherits that whole freight: blood is never merely fluid, it is life out of place.
The interpretive traditions read it by direction. Blood lost, from a wound, from the body, from another, is read toward vitality draining, sacrifice made or injury taken, and the older dictionaries read bleeding toward losses of substance, money, strength or kin. Blood on the dreamer's own hands borrows the waking idiom of guilt so directly that most interpreters simply accept the transfer, Lady Macbeth having fixed the image for the whole culture. Menstrual blood, blood transfused and blood shared in kinship each pull the reading elsewhere, toward cycle, rescue and belonging.
Modern trauma research adds a sober register: blood is common in the repetitive nightmares that follow violence, where it is less symbol than memory. The traditions' readings are recorded here as readings; where blood in a dream is replaying something endured, interpretation gives way to care.