Secondary Polycythaemia

This most commonly occurs as a physiological response of bone marrow to the stimulus of anoxaemia (low levels of oxygen in the blood).

In this condition, as a result of low blood oxygen levels, the bone marrow makes more red blood cells than normal, with a consequent rise in the blood level of both haemoglobin and red blood cells. In healthy people, a hormone called "erythropoietin" (EPO), which is made in the kidney, stimulates the marrow to make red blood cells. When the body is short of oxygen the kidney automatically makes more EPO, which in turn stimulates red blood cell production.

This condition is found in the following circumstances: -

• persons living at altitudes over 10,000 feet.
• chronic pulmonary disease such as emphysema.
• some congenital heart diseases.
• cigarette smokers.
• certain tumours.

Polycythaemia may also be associated with high levels of erythropoietin, e.g., in some patients with renal (kidney) cysts. It may also occur, for unknown reasons, in cases of Cushings Syndrome, hepatoma (primary liver cancer), and hydronephrosis.

The clinical picture in secondary polycythaemia is that of the primary underlying condition.

This variety of polycythaemia is usually beneficial to the course of the underlying condition, and therefore usually requires no treatment.