Differentials
Secondary (reactive) thrombocytosis
SIGNS / SYMPTOMS
People with secondary or reactive thrombocytosis usually have a history of recent surgery, trauma, malignancy, infection, prior splenectomy, and presence of iron-deficiency anaemia.
The thrombocytosis is usually transient and subsides when the primary stimulus ceases. Despite the high platelet count, thrombotic and/or haemorrhagic complications are uncommon.
INVESTIGATIONS
A low serum ferritin level (e.g., <27 picomol/L [<12 nanograms/mL]; varies between guidelines) is diagnostic of iron deficiency, and may explain thrombocytosis.
Elevated inflammatory markers (e.g., the acute phase reactants: CRP, erythrocyte sedimentation rate, fibrinogen) may suggest reactive thrombocytosis.
Spurious thrombocytosis
SIGNS / SYMPTOMS
Patients are typically asymptomatic.
Patients with mixed cryoglobulinaemia may have a temperature-dependent increase in leukocyte and platelet counts when blood samples are tested at temperatures of ≤30°C (≤86°F). A doubling of the platelet count may be noted.
INVESTIGATIONS
Repeat testing at body temperature should be normal.
Familial essential thrombocythaemia
SIGNS / SYMPTOMS
May be no differences in signs and symptoms.
This is a rare disorder that is transmitted in an autosomal dominant pattern so there may be a family history.
INVESTIGATIONS
Genetic testing for mutations in the genes of thrombopoietin and its receptor (c-MPL) can identify familial ET.[26]
Myelodysplastic syndrome (MDS)
SIGNS / SYMPTOMS
Absence of splenomegaly.
INVESTIGATIONS
FBC shows normochromic or macrocytic RBCs and morphological abnormalities such as oval macrocytic RBCs and granulocytes with the pseudo-Pelger-Huet anomaly (hypogranular and hypolobulated granulocytes). Approximately 40% of patients have neutropenia and >30% have thrombocytopenia.
Bone marrow histopathology demonstrates dysplasia in a proportion of undifferentiated myeloblasts.
Prussian blue iron staining of bone marrow aspirate can show ringed sideroblasts; these are abnormal erythroid precursor cells that have granules around the nucleus.
Polycythaemia vera
SIGNS / SYMPTOMS
Aquagenic pruritus (itching after contact with warm water) and plethora.
INVESTIGATIONS
FBC shows erythrocytosis.
Elevated RBC mass, haematocrit, and plasma volume. The total blood volume sometimes increases by twice as much as normal.
Primary myelofibrosis
SIGNS / SYMPTOMS
Anaemia, constitutional symptoms, and bone pain.
INVESTIGATIONS
FBC shows anaemia and/or leukocytosis.
Peripheral blood smear shows leukoerythroblastosis.
Bone marrow biopsy and histopathology shows marrow fibrosis.
Chronic myeloid leukaemia (CML)
SIGNS / SYMPTOMS
May be no differences in signs and symptoms.
Symptomatic patients with CML more commonly present with anaemia, easy bruising, low-grade fever, and susceptibility to infections. The most common physical examination finding in CML is splenomegaly, and the patient may complain of fullness in the left subcostal region.
INVESTIGATIONS
FBC shows that all patients with CML have elevated WBC count and half have a WBC count >100 × 10⁹/L (>100,000/microlitre). A peripheral blood smear shows that most WBCs are neutrophils, but basophil and eosinophil counts are also commonly raised and demonstrate increase in myeloid cells in various stages of maturation. Approximately 45% of CML patients present with anaemia and 15% to 30% have thrombocytosis of >600 × 10⁹/L (>600,000/microlitre).
Cytogenetic testing (fluorescence in situ hybridisation [FISH] or polymerase chain reaction [PCR]) is positive for BCR::ABL1 (Philadelphia chromosome)
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