High Red Blood Cell Count: Causes and Next Steps

The NHS uses the term erythrocytosis, sometimes called polycythaemia, for a high concentration of red blood cells in the blood. Because red cells make the blood thicker, a very high count can slow its flow through vessels and organs, and many of the symptoms are caused by that sluggish flow.

On a full blood count the red cell count rarely stands alone. Lab Tests Online UK explains that haemoglobin and haematocrit usually mirror it, and the NHS says diagnosis rests on the red cell count together with the haematocrit. A mildly high count with normal haemoglobin is often less informative than a high count where all three are raised.

A single high result is not a diagnosis. Lab Tests Online UK lists dehydration, smoking and living at altitude among the everyday reasons for a high result, so context matters before anything more is concluded.

The NHS breaks erythrocytosis into groups depending on the underlying cause, and Lab Tests Online UK gives a parallel list of possible explanations. Taken together they show that the commonest reasons sit outside the bone marrow.

The NHS notes that not everyone with erythrocytosis has symptoms, but many do. It lists headaches, blurred vision, red skin particularly of the face, hands and feet, tiredness, high blood pressure, dizziness, discomfort in the tummy, confusion, bleeding problems such as nosebleeds and bruising, gout and itchy skin after a bath or shower.

Lab Tests Online UK similarly mentions headaches, visual disturbance and a flushed appearance. The itching after a warm bath or shower is a feature people sometimes do not think to mention.

Seek medical help immediately for signs of a clot in the leg or lung, such as a painful swollen leg, breathlessness, chest pain or coughing blood, and call 999 for symptoms of a heart attack or stroke. The NHS identifies these as the serious risks of erythrocytosis.

Lab Tests Online UK notes that a doctor may simply repeat a result that is slightly outside the range, and the context of hydration, smoking and medicines is part of that assessment. The NHS says a GP may refer you to a haematologist for tests to confirm the diagnosis and to find the underlying cause.

Tests the NHS names include a blood test for the changed JAK2 gene and an ultrasound scan of the tummy to look at the kidneys. Lab Tests Online UK also mentions an erythropoietin (EPO) blood test, and notes that in polycythaemia vera the white cells and platelets may be raised too.

If the cause is secondary, the focus moves to the lung, heart or kidney condition behind it. Stopping smoking, losing weight and reducing alcohol are described by the NHS as helping some cases of apparent erythrocytosis.

The NHS says treatment aims to reduce the risk of complications such as blood clots and to treat any underlying cause. Venesection, the removal of about a pint of blood at a time similar to blood donation, is the simplest and quickest way to reduce the red cell number and may be recommended in polycythaemia vera.

In polycythaemia vera, medicines such as hydroxycarbamide or interferon may be used to slow red cell production, and daily low-dose aspirin may be prescribed to help prevent clots. People with apparent or secondary erythrocytosis may be offered aspirin if they also have another health problem affecting the blood vessels.

The NHS adds that, if well controlled, erythrocytosis should not affect life expectancy and that many cases are mild, although polycythaemia vera is more serious and can need long-term treatment.