Yes, a dog does have a specific blood type, although its not the familiar ABO system used to determine human blood type. The actual number of blood type combinations in dogs is still a matter of dispute amongst experts, but the basic blood type test for canines allows for a minimum of eight distinctive results. Some experts suggest that dogs may actually have 12 or more blood types, but only one blood type is considered universally acceptable for unmatched transfusions, a type known as DEA 1.1 negative. Dogs who test negative for another antigen called DEA 4 are ideal donors, but this is the equivalent of finding a rare AB negative blood type in humans.

Blood typing is actually a matter of testing for a reaction to various proteins found on the surface of blood cells. In human blood typing tests, these proteins are designated A and B. Human blood samples react to either A, B, or both. A non-reaction would be considered Type O. In dogs, however, the test for blood type involves at least 7 different blood products, called dog erythrocyte antigens or DEA. A dog's blood sample could show a negative or positive reaction to DEA types designated as DEA 1.1, 1.2, 3, 4, 5 or 7. Of all of these various reactions, one of the most important results is DEA 1.1. A dog which tests negative for DEA 1.1 is considered a good candidate for receiving and donating blood.

Dogs are actually better equipped to handle an accidental mismatch of blood type than humans. Humans have natural antibodies which immediately recognize and attack foreign invaders, including transfused blood cells of a different blood type. Dogs, on the other hand, do not have these natural antibodies to another dog's blood type. If a dog receives unmatched canine blood during an emergency surgery, for example, it may not have a dangerous reaction to the infusion. If more blood is required, however, then a proper cross and type matching must be done. Essentially, a dog gets one free pass when it comes to an unmatched blood type.

For dog owners, the most important thing to know about your dog's blood type is its positive or negative reaction to DEA 1.1. A veterinary can perform a very basic blood test to determine if the dog is DEA 1.1 positive or negative, but more advanced tests for specific blood type may have to be done in a veterinary lab. A DEA 1.1 negative dog can donate blood, since it would be the equivalent of a human donor with type O blood. A DEA 1.1 positive blood type could restrict a dog's ability to donate blood or receive transfusions from other dogs. Transfusing DEA 1.1 positive blood into a DEA 1.1 negative dog could be fatal, but such conditions are very rare.