Full Blood Count Flashcards
What are abnormal full blood count results?
The normal range only includes 95% of the healthy population (2 x SD from the mean).
So, this means that there will be people with normal results that are out of the normal range.
Abnormal results are those that show a big variattion from the expected result.
What do abnormal FBC results mean?
This is often reactive (eg bleeding) rather than reflective of an underlying haematological disorder.
What sources of error are there in pathology results?
Specimen collection - Specimen mix up, wrong blood in tube, Wrong bottle, Pooling sample, Poor technique.
Delivery of specimen to laboratory - specimen delayed / not delivered, wrong delivery method
Specimen analysis and result reporting - specimen mix up, incorrect clinical details, wrong test requested / performed, Inherent test variability, Technical error.
Responsive action - Result not reviewed, Reflex tests not carried out, Right result applied to wrong patient.
What are the essential parameters in the FBC?
Red cells - Indices, RCC, Hb
Platelets - Count, Size
White cells - Count, full differential
What must the sample be mixed with to go into a FBC machine? Why?
Blood samples for FBC must always be placed in a tube containing EDTA and mixed.
EDTA chelates Ca2+ ions and therefore acts as an anticoagulant.
Without a chelating agent the blood sample would clot and be useless for analysis.
The FBC analyser is…
- A Closed system
- Easy to maintain
- Able to cope with high numbers of samples.
Analyser techniques?
Spectrophotometry - amount of light assorted by sample is proportional to the amount of absorbent compound within it.
Flow cytometry - Hydrodynamic focussing.
Flow cytometry differential
What is the packed cell volume? How is it measured?
- Also known as Hematocrit.
- This is the proportion of blood that is made up of RBCs.
- It is used to assess anaemia but more often polycythemia.
- Previously this was measured by centrifuging the blood sample and comparing the height of the red cell fraction with the height of the total blood (this would give the Packed cell volume (PCV)).
- Nowadays, to be compatible with the high throughput required in analysis labs the PCV measurement is replaced by the calculation of multiplying the average red cell size (the mean cell volume (MCV)) by the number of red cells per litre to give the Haematocrit.
How do you measure haemoglobin concentrations>
- Haemoglobin concentration in the blood (I.e. mass / volume) is affected by acute bleed and dehydration.
- Turbidity of plasma can affect the Hb measurement (overestimate).
- It is determined by the lysis of red cells followed by conversion of Hb to a stable form and spectrophotometry.
What is the red cell count? How is it measured and what is it used for?
- Number of RBCs in given volume if blood.
- It is measured by the interruption of a beam of light or electrical current as a single line of cells is passed through a thin tube. White cells are also counted but they are few in number so do not affect the RBC count.
- Used for the assessment of anaemia and erythrocytosis.
What is the mean cell volume?
Average size of the red cells.
This is measured by looking at the amount of light scattered as they pass in a single file past a laser.
This is the most important parameter used to screen for the cause of anemia. It is useful in determining if the anaemia ic microlytic or macrolytic.
What is the red cell distribution width?
- Variation in size of RBC
- If increased, anisocytosis
- Used to help asses cause of anaemia
- -Increased in iron deficiency (The first parameter to rise as iron stores fall)
- -Ususally normal in thalassaemia trait
- -Increased following transfusion
What is mean celll haemoglobin?
- Average measure of the amount of Hb in each RBC (measured in pg (10-15Kg))
- Calcuated by dividing haemoglobin concentration in a given volume of blood by the number of red cells in that same volume.
- Used in assessment of anaemia
- Usually reduced in iron deficiency but normal or increased in macrolytic anaemias.
What is the reticulocyte count?
- Measure the number of young erythrocytes.
- Reticulocytes are counted using special stains or florescent dyes which bind to rRNA (rRNA is not present in more mature red cells).
- It is usefuk in evaluating the different kinds of anaemia.
Why is sample flagged for a blood film?
- Significant result outside of the normal range
- Significant change within the normal range.
- Analyser thinks there are abnormal cells (immature cells, unable to identify, malaria)
A biomedical scientist reviews the results and previous results and clinical details to decide if a film is needed.
