Polycythemia Vera and Essential Thrombocythemia in a General Population

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The summary below is from the full report titled "The Rate of Progression to Polycythemia Vera or Essential Thrombocythemia in Patients with Erythrocytosis or Thrombocytosis." It is in the 16 September 2003 issue of Annals of Internal Medicine (volume 139, pages 470-475). The authors are M. Ruggeri, A. Tosetto, M. Frezzato, and F. Rodeghiero.

What is the problem and what is known about it so far?

Erythrocytosis is a condition in which the number of red blood cells, which carry oxygen, is higher than normal. Thrombocytosis is a condition in which the number of platelets, which are the cells that help blood to clot, is higher than normal. Erythrocytosis and thrombocytosis can be the result of another disease process or diseases called polycythemia vera and essential thrombocythemia. Polycythemia vera and essential thrombocythemia may be associated with such problems as blood clots, bleeding, or serious bone marrow diseases, including some types of leukemia. However, many people with polycythemia vera and essential thrombocythemia never develop problems, and there is uncertainty about the best way to treat these diseases. Studies that have used information from hospital discharge records or cancer registries suggest that polycythemia vera and essential thrombocythemia are rare, occurring in only 1 to 5 of every million people. However, no studies have examined the frequency of these conditions in the general population.

Why did the researchers do this particular study?

To estimate the frequency of polycythemia vera and essential thrombocythemia in a general population.

Who was studied?

10 000 adult residents of Vicenza, Italy, who were participating in a large study of cardiovascular disease.

How was the study done?

In all of the people in the study, a blood count was done at the start of the study and again if results from the first test were abnormal. Patients whose second test confirmed high red cell (erythrocytosis) or platelet (thrombocytosis) counts had further testing to see whether they had polycythemia vera or essential thrombocythemia. The researchers followed everyone for 5 years to see if they developed any complications that might be due to polycythemia vera or essential thrombocythemia.

What did the researchers find?

Of the 10 000 people studied, 1 person had known polycythemia vera, 1 had known essential thrombocythemia, 88 had high red blood cell counts, and 99 had high platelet counts. Of those with high red blood cell counts, the second test confirmed high red blood cell counts in 35 of the 88 and high platelet counts in 8 of the 99 with abnormal first test results. Additional evaluation of these people showed that 2 had polycythemia vera and 3 had essential thrombocythemia. Over the 5 years of follow-up, no patient had a complication. This study suggests that polycythemia vera and essential thrombocythemia occur in about 300 and 400 of every million people, respectively.

What were the limitations of the study?

This study examined only people in a single geographic area and included only people age 18 to 65 years. The frequency of polycythemia vera and essential thrombocythemia may be different in other populations. Also, while no complications were observed, the people were followed for only 5 years.

What are the implications of the study?

Polycythemia vera and essential thrombocythemia may be more common among otherwise healthy persons age 18 to 65 years than previously thought, but complications are uncommon.