• Platelets
• Thrombocytopenia (low platelet count) results from 3 main mechanisms: decreased production, increased consumption/destruction, and abnormal distribution:
Decreased production: due to marrow dysfunction due to primary (e.g. Fanconi anemia) or acquired (e.g. marrow infiltration) causes or ineffective thrombopoeisis (e.g. nutritional deficiency)
Increased consumption or destruction: mediated by enhanced immune response (e.g. ITP, TTP), infection, drug, or shear stress
Abnormal distribution: due to splenic sequestration in hypersplenism or hemodilution
• Thrombocytosis (high platelet count) results from either:
Primary disorders: such as essential thrombocythemia or polycythemia vera
Secondary disorders: such as reactive thrombocytosis (e.g. in response to anemia, thrombocytopenia, inflammation) or induced production by drugs (e.g. growth factors)
Abnormal distribution: or relative thrombocytosis seen in asplenia or hemoconcentration
• Platelet dysfunction (qualitative)
• Platelets are small, anuclear cells derived from megakaryocytes down the myeloid lineage (illustrated above).
• The presence of large platelets (megathrombocytes) might suggest abnormal (e.g. giant platelet disorders) or increased megakaryocyte/ platelet production due to increased destruction (e.g. microangiopathy, ITP) or uncontrolled proliferation (e.g. myeloproliferation).
