Unlike humans, who can be classified into only four blood groups, dogs have more than 13. Among them, DEA-1.1, DEA-1.2, DEA-3, DEA-4, DEA-5, and DEA-7 are the most common ones. Interestingly, as dogs can build antibodies against incompatible blood, they can receive it the first time they receive a blood transfusion. However, after that, they have to receive compatible blood. Otherwise, the dogs could have life-threatening reactions.