The diagnosis of polycythemia, particularly the secondary forms, can be challenging. The distinction between primary and secondary polycythemia is relevant and has management implications. A systematic diagnostic work-up algorithm and a good anamnesis are of paramount relevance. More than one cause may be involved in the development of polycythemia, identifying all of them will be the key to better understanding and eventually solving the polycythemia. We describe a case of a 53-year-old Swiss woman with polycythemia and a high level of carboxyhemoglobin. Her medical story included obesity and obstructive sleep apnea. The anamnesis ruled out the habit of smoking cigarettes, however, the patient reported that she was on a trip to Egypt 10 years before and bought herself a shisha, since then she used to smoke shisha daily, at home, alone. After drastically reducing and then stopping the shisha smoking, 7 months later her blood count and carboxyhemoglobin completely normalized.

The Author(s). Published by S. Karger AG, Basel