My female English Bulldog has blood in her...

[Hawk]

...urine, what could be causing this?

[claudiaa]

Its called 'Heat'Duh.

[macapooh]

ring your vet, they will tell you other signs to look for and may ask you to take her in to have a check up. have you checked that she isn't just in season, is it streaks of blood or clots. tell the vet all the details.