Is there anything that can cause high red blood cells and high risk of stroke?

Good question: 1. Severe dehydration 2. There are some medical conditions in which there is more rbc's like polycythemia. 3. Other are more physiologic, like training at high altitude that atheletes do before performance. Risk of stroke with slugging of rbcs is seen with severe dehydration/polycythemia as well.

Polycythemia vera: Primary conditions are those that increase the replication of red blood cells in the bone marrow, these are known as polycythemias or myeloproliferative disorders. Many secondary conditions exist that can cause high red blod cells as well: including; cancer, altitude, and hypoxic disease to name a few...