What should be considered in health testing?

Those few responsible breeders that do carry out health tests on their potential dogs, will check for genetic illnesses common in that breed, for example Fucosidosis is common in Springer Spaniels, and some breeds their hips are scored.
However are blood tests carried out? As a lot can be revealed in a blood test. If their not, would you urge breeders to have blood tests done on their dogs?
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