The National Health Service of the U.K. states that it is never a good idea to pop a blood blister. By doing so, you invite the risk of infection and compromise the body's natural healing process.
The NHS advises that if a blood blister does burst, do not peel off the excess skin. Clean the area thoroughly, apply antiseptic and a bandage, and change the bandage daily. If the blister has not burst, applying an ice pack immediately after it appears can reduce the pain. A blood blister does not normally require medical attention, but if the blister begins to leak pus, becomes swollen or appear infected, seek out a doctor immediately.