I don't have any advice specifically Helen but just googled "high platelet count" and got this:
"What is thrombocytosis?
Thrombocytosis is a medical term used to describe a high number of circulating platelets in the blood.
Platelets (also called thrombocytes) are small fragments of cells which, following blood vessel injury stick to the damaged vessel wall and to each other forming a major component of the blood clot. T
he platelet count in the blood is normally maintained between 150 and 400 million per ml of blood volume. Many factors can influence an individual's platelet count including exercise and racial origin. In thrombocytosis the platelet count is elevated above 400 million per ml and rarely can reach 5000 million per ml.
What causes thrombocytosis?
A high platelet count can occur in many different medical situations but the two basic processes involved include either an increased rate of platelet production (by the cells within the bone marrow) or by reduced removal of platelets from the blood - which is one of the functions of the spleen.
Most situations that cause thrombocytosis do so by increasing platelet production, whereas reduced platelet removal occurs following surgical removal of the spleen (splenectomy)."
Does that ring any bells with what the GP said?
Has he said what (if anything) will happen next?