Full Blood Count

Obtaining a blood specimen:

An accurate FBC (full blood count) and correct interpretation of a blood film require that an appropriate sample from the patient is collected into EDTA anticoagulated blood and mixed well.  Ideally the concentration  of K2EDTA should be 1.5 - 2.2 mg ml-1.  Blood should be filled to the line to achieve optimum conditions.  Samples should be delivered to the lab without delay as EDTA artefact can affect the results.

Capillary samples in neonates ideally should be collected from the heel.  The first drop of blood should be wiped away to avoid diluting with cleansing materials and cellular debris which can encourage the sample to clot.  The lancet used for skin puncture should be >1.5mm in depth, but not exceed 2.4mm.  Special neonatal tubes should be used as the amount of EDTA is reduced to achieve the optimal concentration for an accurate FBC. For tube information, see the blood sciences tube guide or the tests and tubes database.The Full Blood Count:

The SIEMENS Advia 2120 provides a precise and comprehensive FBC. It provides measurements for haemoglobin, red cell count, red cell indices (size and volume), platelet count and Leucocyte count with full differential (neutrophils, lymphocytes, monocytes, eosinophils and basophils). A Nucleated red cell count is under evaluation and will be added to the repertoire shortly. Additionally, some calculated parameters are provided on the FBC report which are often used to assess iron and thalassaemia status.  A reticulocyte count is available, but does not form part of the routine FBC, this should be requested if required.  The SIEMEMS Advia 2120 has a sophisticated software which examines cells an their physical nature and where appropriate, biomedical scientists are alerted to abnormal cells via a flagging system.  If necessary, the biomedical scientist may respond to this information by requesting a blood film to rule out or confirm more serious abnormalities.

Normal Ranges:

The normal range describes the range where 95% of the normal healthy population will lie.  This also means that there is 5% of the normal healthy population will fall outside the "normal range", however they too are normal.  Normal ranges are a guide.  There are many instances where the FBC will fall outside the "normal range" and yet these could be described as totally normal for the given clinical situation, for example, it is normal for patients who have had a splenectomy to have a moderately raised lymphocyte count or a patient on haemofiltraion to have a raised eosinophil count.  These variations would show as outside the normal range, however they are normal for the situation.  It is very useful therefore for biomedical scientists and haematology clinicians to have appropriate clinical details added to the request so that interpretation  and best clinical advice can be given on the report where appropriate.

Each report from the laboratory will give the appropriate normal range for the age and sex of the patient.  Children have various normal ranges depending on age and sex.  Ethnicity can affect the WBC and platelet normal ranges.  If the patient is Black Afro-Carribean or Black African, the WBC and neutrophils count normal ranges are much lower.  In these instances, the normal adult range must be interpreted depending on the patients ethnic backgound.  If further infomation is required, contact your local laboratory.

Interpretation of a Full Blood Count:

A full blood count must be interpreted with reference to the clinical picture and other pathology results.  Caution must be given to certain abnormal results such as low platelets that may be artefact and repeats should be considered.  The laboratory will usually investigate abnormalities that may be haematological in nature by assessing the blood film (by microscopy) and referring this to haematology clinicians where appropriate.  In the event of serious abnormalities that require urgent attention, such as; acute leukaemia or severe haemolysis, the laboratory staff will allert the On-Call haematology doctors.  Further interpretation information is available via this link.

Page updated: 07/09/2017 Updated by: Daniel Carless