This article is from the Interpretation Of Lab Test Profiles, by Ed Uthman email@example.com with numerous contributions by others.
Polycythemia is defined as an increase in total body erythrocyte mass.
As opposed to the situation with anemias, the physician may directly
measure rbc mass using radiolabeling by 51chromium, so as to
differentiate polycythemia (absolute erythrocytosis, as seen in
polycythemia vera, chronic hypoxia, smoker's polycythemia, ectopic
erythropoietin production, methemoglobinemia, and high O2 affinity
hemoglobins) from relative erythrocytosis (as seen in stress
polycythemia and dehydration). Further details of the work-up of
polycythemias are beyond the scope of this monograph.