RT Book, Section A1 Lichtman, Marshall A. A1 Kaushansky, Kenneth A1 Prchal, Josef T. A1 Levi, Marcel M. A1 Burns, Linda J. A1 Linch, David C. SR Print(0) ID 1189333694 T1 Polyclonal Erythrocytoses (Primary and Secondary) T2 Williams Manual of Hematology, 10e YR 2022 FD 2022 PB McGraw-Hill Education PP New York, NY SN 9781264269204 LK hemonc.mhmedical.com/content.aspx?aid=1189333694 RD 2025/07/20 AB Erythrocytosis, also referred to as polycythemia, is characterized by an increased red cell mass. There is no consensus on terminology as it relates to the choice of erythrocytosis or polycythemia (ie, primary familial and congenital polycythemia but postrenal transplantation erythrocytosis). Herein, the term polycythemia will only be used for polycythemia vera, an acquired clonal disorder caused by somatic mutations (Chap. 42), and polyclonal erythrocytosis will be used for all other states discussed in this chapter.An erythrocytosis can be primary or secondary and can be inherited or acquired.Classification of polycythemic disorders appears in Table 2–2 in Chap. 2.A primary polycythemia/erythrocytosis is caused by somatic or germline mutations within hematopoietic stem cells or erythroid progenitors that result in an augmented response to erythropoietin (EPO). This response is not a compensation for hypoxia and thus is inappropriate for tissue needs.A secondary erythrocytosis is caused by either an appropriate (compensatory) or inappropriate increase in the red cell mass and, in most instances, results from an augmented level of EPO.