A case of pseudothrombocytosis.

Correspondence: Francesca Bonifazi, M.D., Istituto di Ematologia ed Oncologia Medica “L. e A. Seragnoli”, Università di Bologna, via Massarenti 9, 40100 Bologna, Italy. Phone: international +39-051-6363680 – Fax: international +39-051398973 – E-mail: [email protected] A33-year-old man was referred for investigation of thrombocytosis. Over the previous three months he had had two short, transient episodes of headache, visual blurring and paresthesia in the left eye and hand, which were thought to be correlated with a platelet count of 1,500 3109/L. On examination he was well. At the age of 14 months he had been splenectomized because of severe hemolytic anemia with splenomegaly: a presumptive diagnosis of hereditary spherocytosis had been made. From then on, regular blood counts from several laboratories showed only one abnormality, that of platelet values fluctuating around the 9003109/L level. The platelet count, as measured in our laboratory with a Coulter MAXM (Coulter Scientific, Miami, FL, USA), was 8123109/L; the peripheral blood film showed an extreme range and degree of red cell abnormalities with prominent microspherocytosis, micropoikilocytosis, red cell fragmentation and teardrop erythrocytes. Howell-Jolly bodies, a hallmark of the previous splenectomy, were also numerous (Figure 1). It should be noted that many small erythrocytes or fragments were the same size or smaller than platelets and were thus counted, since automated blood counters assess cell populations by their dimensions, as platelets, with a gross overstimation of their real number. A manual count, done in triplicate in a Thoma counting chamber, revealed 5123109/L platelets. A bone marrow biopsy showed a normal number of megakaryocytes, with normal morphology. This person's symptoms were attributed to thrombocytosis, when in fact he had a falsely elevated platelet count, or pseudothrombocytosis. Reported causes of falsely high platelet count have been described after extreme burn injuries,1 in essential mixed cryoglobulinemia,2 in the presence of numerous Howell-Jolly bodies or debris,3 but not in congenital hemolytic anemia. The cause of the patient’s neurologic symptoms remains obscure.