A patient presents with a platelet count of 700 x 109/L with abnormalities in size, shape and granularity of platelets. WBC count is 12 x 109/L, hemoglobin is 11g/d1 and Philadelphia chromosome is absent. The most likely diagnosis would be:

Answer is B (Essential thrombocythemia) : Since all Myeloproliferative disorders can be associated with Thrombocvtosis, Essential Thrombocytosis is a diagnosis of exclusion. The absence of an elevated Haemoglobin makes Polycythemia unlikely (Polycythemia is associated with increased Hb) and the absence of Philadelphia chromosome makes a diagnosis of CML unlikely.. The patient in question has an elevated platelet count (> 600 x 109/L) and only mild elevation of WBC count (12 x 109/L both of which are consistent with a diagnosis of Essental thrombocythemia / thrombocytosis. Essential Thrombocytosis is the single best option of exclusion. Essential Thrombocytosis - CMDT / Robbins Myeloprotiferative Disorders * Diagnosis of exclusion Chronic Myeloid leukaemia * Elevated Platelet count is the hall mark (usually Polycythemia vera >600 x 109/L) Essential thrombocytosis * White cell count is only mildly elevated Myelofibrosis * Haematocrit is normal * Philadelphia chromosome absent Presence of Markedly elevated Platelet count and mild elevation of white cell count in the absence of raised Haemoglobin levels suggests a diagnosis of essential thrombocytosis by exclusion.