I believe with extensive blood work – it can determine if there is a gene mutation. At lease that was the case with my daughter. She also had an ultrasound of the spleen. Another helpful website is MPN Research. A stroke is a concern with excessive platelets. My daughter’s platelets are at 875,000. That is the lowest they have been. Her doctor is positive they will continue to decrease with the interferon. Hope you get answers soon. Waiting is difficult for me.