Thrombocytosis

Question 1

Thrombocytosis - What is it?

Answer 1

Thrombocytosis is an abnormally high platelet count, usually > 400 * 109/l.

Question 2

Causes of Thrombocytosis

Answer 2

Causes of thrombocytosis
reactive: platelets are an acute phase reactant - platelet count can increase in response to stress such as a severe infection or surgery
malignancy
essential thrombocytosis (see below), or as part of another myeloproliferative disorder such as chronic myeloid leukaemia or polycythaemia rubra vera
hyposplenism

Question 3

Essential Thrombocytosis

Answer 3

Essential thrombocytosis

Essential thrombocytosis is one of the myeloproliferative disorders which overlaps with chronic myeloid leukaemia, polycythaemia rubra vera and myelofibrosis. Megakaryocyte proliferation results in an overproduction of platelets.

Features
platelet count > 600 * 109/l
both thrombosis (venous or arterial) and haemorrhage can be seen
a characteristic symptom is a burning sensation in the hands
a JAK2 mutation is found in around 50% of patients

Management
hydroxyurea (hydroxycarbamide) is widely used to reduce the platelet count
interferon-α is also used in younger patients
low-dose aspirin may be used to reduce the thrombotic risk

Question 4

Thrombocytosis - Example Question

Answer 4

A 46-year-old female patient of yours is seen in the outpatient family practice clinic, and is found to have a platelet count of 800 x 10³/microliter on routine testing of her full blood count. After a specialist review, she is diagnosed with essential thrombocythaemia after discovering she is JAK2 positive. She is asymptomatic has no history of arterial or venous thromboses. What is the next step in management?

	Hydroxyurea
	Aspirin
	> No management required
	Prophylactic enoxaparin
	Platelet pheresis

The commencement of therapy for someone with essential thrombocytosis comes down to separating patients into high risk and low risk.

Low risk features (no treatment):
Platelet count below 1,000 x 10³/microliter
No history of thromboses
No risk factors for thrombosis

Essential thrombocytosis is a chronic myeloproliferative disorder that is frequently asymptomatic. It simply leads to an increased platelet count, typically of non-functional platelets.

Note that the concern about platelet counts above 1,000 x 10³/microliter is because of haemorrhage instead of thromboses, because the platelets are essentially non-functional.

Question 5

Low risk Thrombocytosis

Answer 5

The commencement of therapy for someone with essential thrombocytosis comes down to separating patients into high risk and low risk.

Low risk features (no treatment):
Platelet count below 1,000 x 10³/microliter
No history of thromboses
No risk factors for thrombosis

Essential thrombocytosis is a chronic myeloproliferative disorder that is frequently asymptomatic. It simply leads to an increased platelet count, typically of non-functional platelets.

Note that the concern about platelet counts above 1,000 x 10³/microliter is because of haemorrhage instead of thromboses, because the platelets are essentially non-functional.