Reactive Thrombocytosis Caused by Infection

James L. Chen, Khosrow Afsari, MD


Infect Med. 2002;19(10) 

In This Article

Abstract and Introduction

In adults, infection is the most frequent cause of thrombocytosis, an abnormal elevation of platelet counts. Patients with reactive thrombocytosis generally are asymptomatic. However, in a small proportion of cases, especially in elderly patients or those with symptomatic atherosclerosis or thrombotic disease or immobility, thrombosis results. Treatment of the underlying disease should lead to resolution of reactive thrombocytosis. We present a case of reactive thrombocytosis and discuss a possible mechanism for the disease.

Thrombocytosis, or an abnormally high number of platelets in the circulating blood, can be attributed to many causes. Platelet counts can be elevated as a result of abnormal proliferation of megakaryocytes. This is known as primary (essential) thrombocytosis or thrombocythemia and is part of the spectrum of myeloproliferative disorders.[1] However, most cases of thrombocytosis are reactive, or secondary, thrombocytosis, which occurs as a result of other disease.[2]

A recent 1-year prospective study of 777 Saudi Arabian patients with platelet counts greater than 500,000/µL showed that 21% of the thrombocytosis cases were caused by infection, 19% involved rebound (after bleeding, iron deficiency, or cancer chemotherapy), 18% were a result of tissue damage, and 13% were due to chronic inflammation. Malignancy, splenectomy, and myeloproliferative disorders each accounted for fewer than 5% of cases.[3]

In a 1994 study by Buss and colleagues[4] of patients with platelet counts greater than 1 million/µL, reactive thrombocytosis was the major cause in 82% and myeloproliferative disorders in 14%; the cause was idiopathic in 4%. The most common cause of reactive thrombocytosis was infection (31%), followed in descending order by splenectomy (19%), malignancy (14%), and trauma (14%).


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