Polycythemia or Erythrocytosis is where there is a high concentration of red blood cells in your blood.  This makes the blood thicker, less viscous and less able to travel through blood vessels and to organs impeding oxygen delivery. This is obviously a huge problem with those who already suffer with conditions like COPD where oxygen delivery is already hindered.

Symptoms of mild cases include:
•    Headaches
•    Blurred vision
•    Red skin
•    Tiredness
•    High blood pressure
•    Dizziness
•    Abdomen discomfort
•    Confusion
•    Nose bleeds and bruising
•    Gout
•    Itchy skin (especially after a bath, as a result of the high levels of white blood cells releasing the chemical histamine)
The slow, sluggish blood flow associated with Polycythemia can also cause blood clots, which can put you at risk of heart attacks, pulmonary embolisms (blockages in a vessel), Deep-Vein Thrombosis (DVT) or Strokes.
Signs of this include:
•    Pain, swelling, redness and tenderness in your legs
•    a heavy ache in the affected area
•    Warm skin in the area
•    Breathlessness
•    Chest/upper back pain
•    Coughing up blood
•    Feeling dizzy or light-headed
•    Fainting
Apparent Polycythemia is where your red cell count is normal but the concentration of red blood cells is higher due to a lack of plasma in the blood making it thicker. Usually caused by being overweight, smoking, excessive drinking or from certain medications like diuretics.  It can be improved if the underlying condition is treated.
Absolute Polycythemia is where your body is actually producing too many red blood cells. Primary Polycythemia is where your bone marrow is producing too many due to a genetic defect in the JAK2 gene and is known as Polycythemia Vera (PV).  Secondary Polycythemia is where too many red blood cells are produced but is caused by an underlying condition.
Secondary Polycythemia can be caused by kidney disease or tumours but also by COPD and Sleep apnoea which can cause an increase in Erythropoietin to be produced by the kidneys which stimulates the bone marrow to produce more red blood cells.  This is a reaction to there not being enough oxygen reaching the kidneys.
The treatment aims to prevent symptoms and complications such as blood clots from occurring and to treat any underlying causes so will vary slightly from patient to patient.
Venesection is the quickest and simplest way of reducing the number of red blood cells.  It involves removing about one pint of blood at a time, in a similar way to giving a blood donation. The frequency could be anywhere from one a week to once every 6-8 weeks depending on cause and severity.
Medications such as interferon to reduce red blood cell production and those to prevent blood clots such as aspirin may be administered. Or any medication that treats the underlying cause may be given.
The outlook depends upon the underlying cause but most cases are mild and easily managed, although PV can be more serious.
If you have Polycythemia, it is important to take any medication you are prescribed and keep an eye out for signs of possible blood clots to help reduce your risk of serious complications.
Continuous low-flow oxygen therapy can also help to relieve Polycythemia. As increased oxygen supply to the kidneys will reduce the amount of erythropoietin they release and therefore prevent an increase of red blood cell production in the bone marrow and also helps to relieve associating symptoms.
References: http://www.nhs.uk