Polycythemia vera (PV) is a chronic myeloproliferative disorder in which the red cells are the predominating lineage. Here are some typical student questions along with my answers.

Q. Are the erythrocytes in PV normal?

A. No, they aren’t considered normal because they come from a malignant clone of erythroblasts. But they do carry oxygen, and they do act and look like benign RBCs. They’re just the end stage of a malignant erythroblast’s development.

Q. How come the oxygen saturation is normal in PV?
A. You use the oxygen saturation to tell apart primary polycythemia (polycythemia vera) from secondary polycythemia. In secondary polycythemia, the oxygen saturation is usually low (that’s why the patient is making so many red cells – he or she needs to create more oxygen carrying capacity! Maybe the patient lives way up in the mountains or something.). In contrast, the oxygen saturation is normal in polycythemia vera, because the malignant RBCs are simply carrying the oxygen that happens to be around (and they carry it the same way benign RBCs do), and unless the person with polycythemia vera happens to live way up in the mountains and smoke (pretty unlikely), the oxygen saturation in that person should be normal.

Q. Does the test for RBC mass necessarily tell you whether the red cells are benign?
A. The test for RBC mass and the plain old red blood cell count (RBC) that you get in a CBC do not differentiate between benign mature red cells and the malignant mature red cells you see in polycythemia vera. So patients with any kind of polycythemia (whether it’s primary or secondary) will have an increased RBC mass/increased RBC.