Haematology in MRCP-Polycythaemia

Haematology in MRCP(1)- Polycythaemia

I am going to talk about a few important topics that are frequently asked in haematology, MRCP. The first topic that I want to talk about is polycythaemia.

Polycythaemia or erythrocytosis is defined as an increased concentration of red cells, usually with a corresponding increase in hemoglobin level.

I find the following classification of polycythaemia useful and easy to remember.


There are two main types of polycythaemia- Relative polycythamia ( pseudopolycythaemia) or absolute polycythaemia ( true polycythaemia).

Relative polycythaemia means that the absolute red cell counts are normal but due to haemoconcentration because of decreased plasma volume, patient’s haemoglobin is raised. This can be due to any kind of dehydration, however, there is a popular condition often asked in MRCP, it is an obscure condition of unknown origin known as Gaisbock’s syndrome (stress polycythaemia). It is a kind of relative polycythaemia.

For true polycythaemia, the absolute red cell counts are raised and it can be subdivided into either primary ( without obvious reason) or secondary ( with an underlying reason). For primary cause, the most important disease you must learn is polycythaemia rubra vera which I will cover in my future post. For secondary polycythaemia, the haemoglobin can be raised appropriately ( due to increase physiological need) or inappropriately.

There are three common tumours that cause secondary polycythaemia- namely renal cell carcinoma, hepatoma and hemangioblastoma ( very popular question in MRCP!). As for the examples of appropriate secondary polycythaemia, the causes are easy to remember because patients with all these conditions are hypoxia chronically, therefore they need an increase haemoglobin level to survive!