Some patients with polycythemia rubra vera (PRV) may initially show thrombocytosis or a nondiagnostic increase in hemoglobin and hematocrit. These patients may be "masked" before overt PRV is evident.

An initial thrombocytosis may cause the patient to be confused with essential thrombocytthemia.


Features of masked polycytemia:

(1) JAK2 mutation

(2) bone marrow morphology consistent with polycythemia

(3) one of the following:

(3a) hemoglobin >= 16.5 g/dL or hematocrit >=49% in men

(3b) hemoglobin >= 16.0 g/dL or hematocrit >=48% in women

(4) failure to meet criteria for overt PRV


Risk factors for worse outcome:

(1) age > 65 years

(2) white blood cell count > 15 * 10^9/L


A patient without these risk factors has the same survival as a patient with over PRV.


Additional findings:

(1) some patients may show increased bone marrow fibrosis

(2) complications include thrombosis and major bleeding

(3) a patient with masked PRV may show a more frequent complete response to therapy

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