The rate of progression to polycythemia vera or essential thrombocythemia in patients with erythrocytosis or thrombocytosis.
BACKGROUND
The clinical relevance of mild erythrocytosis (hematocrit > 0.48 in women or > 0.51 in men) or thrombocytosis (platelet count > 400 x 10(9) cells/L) in asymptomatic persons is uncertain.


OBJECTIVE
To estimate the frequency of polycythemia vera or essential thrombocythemia in persons with erythrocytosis or thrombocytosis in a general population.


METHODS
Cohort study.


METHODS
Vicenza, Italy.


METHODS
10 000 community dwellers age 18 to 65 years and enrolled in the Vicenza Thrombophilia and Atherosclerosis project.


METHODS
Platelet count and hematocrit at baseline in all participants and at second follow-up if baseline results were abnormal. Measurement of erythrocyte sedimentation rate, peripheral arterial saturation, serum erythropoietin level, and leukocyte alkaline phosphatase level; chest radiography; abdominal ultrasonography; and occult fecal blood testing were done in persons with confirmed high hematocrit or platelet counts. Polycythemia vera and essential thrombocythemia were diagnosed according to the Polycythemia Study Group criteria.


RESULTS
At baseline examination, 1 person had polycythemia vera, 1 had essential thrombocythemia, 88 had erythrocytosis, and 99 had thrombocytosis. Second examination confirmed erythrocytosis in 40% (95% CI, 29% to 51%) and thrombocytosis in 8% (CI, 4% to 15%) of those with abnormal baseline results. Among persons with confirmed abnormalities, further evaluation revealed 11 with idiopathic erythrocytosis, 2 with polycythemia vera (3/10 000 [CI, 0.6 to 8.7/10 000]), and 3 with essential thrombocythemia (4/10 000 [CI, 1.09 to 10.2/10 000]). After 5 years of follow-up, 1 additional person with a high platelet count developed essential thrombocythemia, and no persons developed hemorrhagic or thrombotic complications.


CONCLUSIONS
The prevalences of polycythemia vera and essential thrombocythemia were higher than expected in this general population. However, the risks for developing polycythemia vera, essential thrombocythemia, or associated vascular complications in persons with erythrocytosis or thrombocytosis were low.
D000293:Adolescent; D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006400:Hematocrit; D006801:Humans; D007558:Italy / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D010976:Platelet Count; D011086:Polycythemia / Q000150:complications*; D011087:Polycythemia Vera / Q000175:diagnosis / Q000453:epidemiology*; D015995:Prevalence; D012307:Risk Factors; D013920:Thrombocythemia, Essential / Q000175:diagnosis / Q000453:epidemiology*; D013922:Thrombocytosis / Q000150:complications*