Check erythropoietin level.
=> If low or very low normal, obtain Jak-2 and place a Hematology clinic consult.
=> If wnl or elevated epo level, then that essentially rules out primary polycythemia (P. vera), and I'd recommend checking an ABG.
=> If carboxyhemoglobin elevated, then I would suspect tobacco use, but could also check urine cotinine. Sleep apnea always a possibility.
=> If primary polycythemia is ruled out, there is no strong role for therapeutic phlebotomy, unless Hct rose above 55% and symptomatology. In such a scenario, limited ther. phlebotomy may be beneficial, to get the Hct below 55% again, but that wouldn't replace smoking cessation or CPAP (depending on cause). Occult malignancies always a possibility, but the w/u starts with the epo level.