Normal platelet count <450 × 109/L; platelet counts >1000 × 109/L may cause thrombosis or bleeding when platelets are dysfunctional.
Almost always, thrombocytosis in infants and children is reactive. Increased production occurs with
·Acute or chronic infection.
·Acute or chronic haemorrhage.
·Trauma or surgery.
·Iron deficiency anaemia.
·Certain malignancies, e.g. Wilm’s tumour.
·Any inflammatory disease, e.g. ulcerative colitis.
·Primary myeloproliferative disorder, e.g. essential thrombocytheaemia (ET) or in association with chronic myeloid leukaemia (CML).
Post-splenectomy. On examination look for signs of iron deficiency anaemia, bruising or bleeding, splenomegaly, signs of Kawasaki’s disease and general ill health. The most common scenario is for the child to be totally well having recovered from an acute infection and a follow-up FBC shows a raised platelet count.
·FBC: e.g. WCC ‘rise’in infection or signs of iron deficiency anaemia.
·CRP/ESR: ‘rise’in inflammatory/malignant conditions.
·Bone marrow aspirate only ever indicated if primary myeloproliferative disorder (MPD) such as essential thrombocytheaemia is suspected (which is very rare).
·Treat underlying cause.
·Watch and wait in reactive cases, as requires no treatment.
·Give aspirin in Kawasaki’s disease (one of the few indications for aspirin in children).
Reactive thrombocytosis generally has an excellent prognosis. Primary causes are very rare and have a variable prognosis. They are best managed by a paediatric haematologist.