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Abnormal Blood Count Values and Anaemia

The ‘Full Blood Count’ gives haematology doctors detailed information about different parts of the blood. It is common for GPs to request a full blood count test when patients are unwell, or as part of health screening as it gives valuable information about someone’s health. The three main parts of the blood count are the haemoglobin levels, white cell count and platelet counts.

The commonest problem with haemoglobin is ‘anaemia’ which is due to abnormally low haemoglobin. Haemoglobin is the main constituent of red blood cells – the cells that travel around the body taking oxygen to tissues. Anaemic patients may have few specific symptoms, but as anaemia gets worse, most patients notice tiredness, shortness of breath on exertion, ringing in the ears and headaches.

Anaemia is always due to one of three broad reasons. Reduced production of haemoglobin from the bone marrow, increased loss of red cells from part of the body, typically abnormal bleeding, or destruction of the red cells by the body. Anaemic patients commonly present to many different medical specialists, as there are many reasons why patients lose, destroy or fail to make red cells adequately. On occasion, anaemic patients require a bone marrow biopsy to help explain the cause of the anaemia. Depending on the cause of the anaemia, there are many different treatments. Some patients will require transfusion of red blood cells.

More rare are a range of conditions where patients make too much haemoglobin. These conditions are broadly known as the ‘Polycythaemias’. They may be due to an underlying bone marrow problem (Polycythaemia Rubra Vera), or occasionally due to other general medical factors such as smoking or chronic lung disease. Patients with these conditions may require excess blood to be taken off, known as venesection, or some patients even need specific tablet treatments to ‘damp down’ the over active bone marrow.

The white cells are the body’s soldiers, that patrol the blood and lymphatic system ready to fight invading pathogens such as viruses / bacteria / fungi etc. There are many different types of white cell with very different roles in the normal immune response. They range from cells which look granular under the microscope (granulocytes), such as neutrophils, monocytes, eosinophils, basophils etc to more specialised cells called lymphocytes and natural killer cells. The white cell count can go up or down due to a range of medical conditions, such as infection, and this can be a completely normal response. Indeed, the majority of patients with slight abnormalities of their white cell count do not have a blood disorder. There are, however, other more serious causes of elevated and lowered white cell counts, including leukaemia, which is why abnormalities of the white cell count are usually either followed closely or investigated further if they do not resolve.

Platelets are tiny cells that are present in the blood in large numbers – a healthy individual is likely to have over 150,000,000,000 platelets per litre of blood. They act as plugs that stick together at the site of bleeding. This helps the clotting system to make a blood clot that is stable and stops us from bleeding excessively after injury.

Patients with low platelet counts tend to bruise more easily and may experience nose bleeds, or bleeding in their mouth or gums (so called ‘mucosal bleeding’). On occasion, bleeding due to a low platelet count can be serious. Patients with abnormally high platelet counts may be at increased risk of blood clotting disorders, particularly stroke.

A low platelet count (thrombocytopenia) is frequently caused by destruction of the platelets, most commonly due to a condition called idiopathic thrombocytopenic purpura, or ITP for short. Another cause for low platelets can be the failure of the bone marrow to make adequate numbers of cells. There are tests that can help separate these two causes, but on occasion, patients with a low platelet count will need a bone marrow biopsy to establish the cause of the problem. Treatment will depend on the underlying cause. 

A high platelet count (thrombocytosis) may be a normal reactive response to other medical conditions, such as infection or bleeding. On occasion, however, the bone marrow can be over active and produce too many platelets by mistake. This condition is usually one of the myeloproliferative disorders termed ‘Essential Thrombocythaemia’.