86 Essential Thrombocythemia (ET)

Michelle To and Valentin Villatoro

Image of peripheral blood smears showing a giant platelet (center) and an increase in the number of platelets seen in Essential Thrombocythemia. From MLS Collection, University of Alberta.

Image 1: 50x oil immersion. https://doi.org/10.7939/R3J09WK51

Image 2: 60x oil immersion. https://doi.org/10.7939/R3X63BM52


Affected Cell Line: Megakaryocytes, Platelets.1,2


Mutation: JAK 2 V617F, CALR, and MPL gene mutations.1,3


Age Group Affected: Diagnosed most commonly at 50-60 years old.1


Clinical Features:

Most patients are asymptomatic and present with a platelet count of ≥450  x109/L.1 Thrombosis, vascular occlusion, and bleeding problems are the most commonly associated complications. Despite having abundant platelets, they are often dysfunctional.


Laboratory Findings for ET:1,4,5


WBC: Normal to Slightly Increased

PLT: Increased (often 1000-5000  x109/L)

Hb: Slightly Decreased

Hct: Slightly Decreased

MCV: Normal


RBCs, are normocytic and normochromic

Marked thrombocytosis


Abnormal platelet morphologies:

Giant, agranular, clumping, and irregularly shaped


Hypercellular due to increased megakaryopoiesis

Abnormal megakaryocyte morphology: Clusters, Enlarged,


Other Tests:

Platelet function tests: abnormal

Reactive Thrombocytosis

A non-malignant condition that involves an increased platelet count secondary to other conditions that result in an increase in platelet production. It is associated with infections and inflammatory processes.5


Reactive thrombocytosis can be differentiated from essential thrombocythemia by looking at the platelet count. Platelet count rarely reaches >1000  x109/L and platelet function tests are  normal.5


1. Swerdlow SH, Campo E, Harris NL, Jaffe ES, Pileri SA, Stein H, et al. editors. WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues Volume 2. 4th ed. International Agency for Research on Cancer (IARC); 2008.

2. Schaub CR. Chronic Myeloproliferative disorders I: chronic myelogenous leukemia. In: Clinical hematology and fundamentals of hemostasis. 5th ed. Philadelphia: F.A. Davis Company; 2009. p. 371-84.

3. Choi CW, Bang S-M, Jang S, Jung CW, Kim H-J, Kim HY, et al. Guidelines for the management of myeloproliferative neoplasms. Korean J Intern Med [Internet]. 2015 Nov 30 [cited 2018 Jul 9];30(6):771–88. Available from: http://kjim.org/journal/view.php?doi=10.3904/kjim.2015.30.6.771

4. Randolph TR. Myeloproliferative neoplasms. In: Rodak’s hematology clinical applications and principles. 5th ed. St. Louis, Missouri: Saunders; 2015. p.561-90.

5. Randolph TR. Myeloproliferative neoplasms. In: Clinical laboratory hematology. 3rd ed. New Jersey: Pearson; 2015. p. 450-78.


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Essential Thrombocythemia (ET) Copyright © 2019 by Michelle To and Valentin Villatoro is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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