Since your vet thinks the blood sample sat around for a while, then the platelets in the sample probably began to stick to each other, forming a clot in the tube. Then when they looked at the sample to get a platelet count, the number appeared lower than it should've. If that was the case, then the low platelet count was just an inaccuracy, not something wrong with your dog. When he goes in for his neuter, I'm sure the vet will check the new specimen right away, and that will give you an accurate count. This actually happens occasionally at any hospital when the specimen tube is either filled up too much or if it sits around too long. Usually the lab notices that there are clots in the specimen and they throw it out, but sometimes they give a false low count. I hope thats the case with your bubs.