Medical Fun Facts Podcast

MFF0060: Full blood examination

It’s Thursday 27 April 2017.

Tonight, I want to venture a little out of my area of knowledge into the discipline of hæmatology.

One of the most common referrals to a pathologist is for a full blood examination. A specimen of blood is collected in a tube containing an anticoagulant known as EDTA. The tube usually has a lavender coloured bung. Unlike chemical pathology, the focus in hæmatology is the cellular component of blood. In a full blood examination, hæmatology pathologists and medical laboratory scientists, look at the erythrocytes or red blood corpuscles, the white blood cells or leucocytes and the platelets.

The erythrocytes contain hæmoglobin and carry oxygen for cellular respiration. The leucocytes are part of your immune system and help fight infection. The platelets help clot the blood and assist in controlling hæmorrhage.

In a FBE, the erythrocytes, leucocytes and platelets are counted. The ratio of erythrocytes to plasma is measured, to get the hæmatocrit. The various types of leucocytes are counted and a differential calculated. The hæmoglobin level in the erythrocytes is measured. The average size of the red blood corpuscles is measured. If the automated analyser signals something abnormal, a medical laboratory scientist will make a smear and review the blood film. If there’s something very odd, then a hæmatology pathologist will make a final review before a result is authorised.

Given the complexity of blood, all sorts of things can go wrong. Let’s have a look at some examples.

Low red blood corpuscles and hæmoglobin means anæmia and could be due to many things including iron deficiency or hæmorrhage. High levels mean polycythæmia and is associated with some kidney disease, some lung disease and living at high altitude.

A low number of white blood cells is called leucopænia and happens with some viral infections, some bone marrow disorders and when patients receive chemotherapy. High white cell counts are often associated with bacterial infections and some inflammatory conditions.

A low platelet number is known as thrombocytopænia and is seen when some drugs are taken as well as some viral infections and autoimmune conditions. Thrombocythæmia is when the platelet count is too high and is associated with some infections and inflammatory diseases.

Looking at a blood smear is important for diagnosing the presence of parasites like plasmodia which cause malaria.

The full blood examination is a really important part of a patient workup and in some situations, especially in critical care patients, a full blood examination may be requested daily to monitor changes in a patient’s condition.

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