Episode 9: Thrombocytosis


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Author: Dr. Terance Lee
Editor: Dr. Suneet Sood
Narrators: Thong Yi Kun, Alan Koay


Today, we are here to share a case which involves the hematological system.

We have a 55-year-old male who presented with persistent fatigue and intermittent dizziness. The doctor immediately noticed that he was pale. He reported no other symptoms such as loss of weight, fever, changes in bowel habit or bloody stool. The treating doctor started an anemia workout by ordering a complete blood count. While the results were consistent with a case of anemia, the team was taken aback with the platelet count. It was over approaching 1,000×10^9  /liter.

That is an extremely high platelet level!

In fact, it is referred as extreme thrombocytosis in a platelet count of more than 1000 x 109/L. An elevated platelet count is any value above 450 x 109/L, which we call thrombocytosis.

What can cause such a high platelet count?

To explore the causes of thrombocytosis, we can categorize them into two groups – clonal thrombocytosis and reactive thrombocytosis.

Clonal thrombocytosis refers to the autonomous proliferation of platelet cells in patients with myeloproliferative or myelodysplastic disorders, namely essential thrombocythemia, polycythemia vera, primary myelofibrosis and chronic myeloid leukemia

Reactive thrombocytosis is thrombocytosis secondary to a variety of medical or surgical conditions. Common examples are recent surgery, trauma, infection, malignancy and iron deficiency. The reactive form is usually self-limiting when the precipitating factor is resolved when possible.

How should we approach a case of high platelet count like what happened in this patient?

First and foremost, we would have to consider the possible complications of having a high platelet level and our number one concern will be thrombotic complications. Thrombotic events may manifest with symptoms such as headache, syncope, chest pain or more sinister complications such as stroke and myocardial infarction. Bleeker and Hogan, in 2011, reported that thrombotic complications are usually the major causes of morbidity & mortality in clonal thrombocytosis especially in essential thrombocytosis or polycythemia vera. Antiplatelet therapy may likely be initiated in these cases. On the other hand, thrombotic events are rare amongst patients with reactive thrombocytosis, and one large case series only reported an incidence of 1.6%.

I presume the risk will be higher in patients with other contributing risk factors such as recent surgery or trauma?

Yes. This is one of the reasons why it’s important to investigate for the cause so we can assess patient’s risk of developing a thrombotic event. If it’s a reactive thrombocytosis, we would have to just solve the underlying precipitating condition.

So, how did the medical team for this patient move forward from the result?

Due to the very high platelet count, the team was at one point determined to seek haematology referral and arrange bone marrow biopsy with a provisional diagnosis of essential thrombocytosis. In fact, the chief resident was already considering therapy with hydroxyurea, an anticancer drug. But then the senior consultant saw the case, and reminded his team that in any thrombocytosis, it’s important to rule out iron deficiency anemia.

This patient did have low haemoglobin

Yes, this patient had low hemoglobin. If we make a quick correlation with all the findings so far, one explanation is that the thrombocytosis is a reactive form and caused by iron deficiency. The team ordered iron studies and the patient was indeed deficient in iron. Iron therapy was initiated and both the hemoglobin and platelet levels gradually improved.

It was a case of extreme thrombocytosis due to reactive thrombocytosis. That was fortunate! The team managed to prevent an unnecessary invasive procedure in this case.

Yes. If we encounter a patient with thrombocytosis, it is suggested that we should always start with less invasive tests. A repeat platelet count and peripheral blood smear is advisable to confirm the result. If we recall the causes of reactive thrombocytosis; besides iron deficiency, other causes such as infection and tissue damage are inflammatory in nature. Thus, we can quickly send blood for inflammatory markers such as C-reactive protein & ESR; together with the iron studies. These blood tests do not take too much time for us to rule out these common causes. It’s usually not too late to only consider more invasive tests after reactive thrombocytosis has been ruled out.

Wow, I guess this case taught me that I should not be completely distracted from the initial presenting complaint simply because of a shocking and unexpected result. Once you’ve shared the information pertaining to the platelet count, I was drawn into it and didn’t realize I have neglected the issue of anemia. The patient’s presenting issue turned out to be the answer to the unexpected finding of thrombocytosis.

You’ve illustrated an important point right there. It’s justifiable for the team to be concerned of the high platelet level due to the possible complications and to manage that issue accordingly. But if the anaemia workout was continued concurrently, clinicians would be able to discover the case of iron deficiency and have the opportunity to correlate it with thrombocytosis.

That’s great! We found the cause and it’s a much treatable condition.

Yes, it turned out we were dealing with iron deficiency. But we should not rest on our laurels with this diagnosis. There must be a cause for the iron deficiency and we must explore further. In this patient’s age group for example, I would be worried about a chronic blood loss causing iron deficiency. Chronic GI bleed is a rather common cause of blood loss and a further investigation is integral. It’s a rather long process to get to the root of the problem but it’s all for the benefit of the patient.

So our final message is: if a patient has thrombocytosis, always exclude iron deficiency anemia.



  1.      Bleeker JS, Hogan WJ. Thrombocytosis: diagnostic evaluation, thrombotic risk stratification, and risk-based management strategies. Thrombosis. 2011 Jun 8; Article ID 536062
  2.      Chandna A, Sharma J, Sangwaiya A, Samal S, Sankala M, Garg S. Case report: iron deficiency anaemia with thrombocytosis: a diagnostic challenge. IJHBR. 2014 Oct;3(1):43-6.
Episode 8: Drug Interactions
Episode 10: Differential Cyanosis

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