sorry typo, meant blood transfusion not test.
Gill as with humans they have types of blood. More than we humans have (specific number for dogs and cats but i'd have to look it up as i cant remember it)
As you probably know with humans its very important to match the type of blood, if in doubt and you had to give some blood i think the type O (or whichever one is the most common - like me lol) is the safest to give coz its a better bet than the person needing it may also have that type and also (i think but not certain on this) it may be less likely to cause such severe reactions.
Now with dogs, the way their body and immune system work you could give a dog any type of other dog blood and it would be ok, Only if you then gave that dog yet another unmatched blood transfusion would it run into problems (to do with the antibodies etc - its actually a very complicated response that goes on but coz they;ve had foreign blood already they will then have antibodys to attack any future foreign blood so its really important to then give them blood that the body will think is its own)
In cats however they are apparently very sensitive and you dont get the luxury of a first time being ok as the majority of them will have almost immediate physalogical response and can rapidly lead to death (some may be lucky of course as every living body is individual) so in an emergency situ no i wouldnt advise any one to let their cat be given unmatched blood , but then it isnt so clear cut as that when that emergency situ arises and of course the vet usually knows best or would know nothing could be done if the cat was dying in front of your eyes and you didnt have a clue why. That situations are extremely rare (thankfully) and normally even in emergencys the owners or veterinary staff have a fairly good idea why and if not usually normal testing points to certain likely directions.
I of course researched this many years ago but will have to go and do so again tomorrow as i'm off out taking kids to their halloween parties.
What i will say though is if blood banks were to be more freely available in more normal practices then we would have to make the choice to have our cats blood type tested at an early age so it was on their records as that cannot be done (as far as i know) in normal practice and would have to be sent away to lab, so in emergency you'd want that info to hand.