Introduction: Thrombocytosis is a common condition in infancy and childhood. There are very few paediatric literature on its incidence and clinical significance.
Method: We conducted a prospective study over 18 months (January 1993 to June 1994) on all patients admitted with a platelet count done. Cases with platelet count > 600 x 10(9)/L were reviewed and followed-up. Serial platelet count were done at 1 week, 2 weeks, 3 weeks, 4 weeks, and then monthly until it normalised.
Results: One hundred and thirty-five cases out of 10,288 admissions had raised platelet count. There was a preponderance of male (sex ratio M:F = 1.7:1). Majority was less than 1 year old. Seventy-eight percent had associated infection of which 2/3 were due to bacterial infections, Pneumonia was the most common bacterial infection associated with thrombocytosis whilst gastroenteritis was the most common cause for non-bacterial infection and Kawasaki's disease constituted the majority of the non-infective etiology. Cases with platelet count > 900 x 10(9)/L, 73.3% were due to bacterial infection. Three cases of Kawasaki's disease had platelet counts > 900 x 10(9)/L. Fifty-two percent of cases developed thrombocytosis within 4 days of illness. In nonbacterial infection, the thrombocytosis normalised by about 1 week after onset. For bacterial infection, the thrombocytosis normalised later depending on the severity of infection. In majority of the Kawasaki's disease, the platelet count normalised by the third week.
Conclusion: Primary thrombocytosis is rare in paediatric age group. None of the cases developed any symptoms associated with thrombocytosis. Secondary thrombocytosis is a benign and common phenomenon in children.