What does a high hemoglobin mean?

Polycythemia: There are only a few causes of a high hemoglobin. We divide these cases into primary and secondary high hemoglobin, or "polycythemia." secondary means caused by heart disease, hypoxemia, tobacco, sleep apnea. Primary means a benign blood disease called polycythemia vera. A hematologist can usually determine which type of polycythemia a patient has.