6. Interpreting the full blood count Flashcards
What is a full blood count ?
A “full blood count” (FBC) is the term used to refer to a panel of tests routinely performed on a blood sample in order to determine whether or not any haematological abnormalities are present.
These test are performed in the lab on automated analysers capable of processing many hundreds of samples in a day.
List the 10 tests involved in a full blood count analysis
- White blood cell count (WBC)
- Red blood cell (RBC)
- Haemoglobin concentration (Hb)
- Haematocrit (HCT)
- Mean Cell (or corpuscular) Volume (MCV)
- Mean Cell Haemoglobin (MCH)
- Platelet Count
- Reticulocytes
- Differential white blood cell counts
- Blood film
Explain what a White blood cell count is (WBC)
A WBC is used to count the amount of white blood cells present within a patient.
Its determined by automated cell counting (interruption of a beam of light or electrical current as a line of single cells flow through a narrow tube) after the red blood cells have been lysed in the sample.
Explain what a Red blood cell count is
A RBC is used to count the amount of red blood cells present within a patient.
Its determined by automated cell counting (interruption of a beam of light or electrical current as a line of single cells flow through a narrow tube).
White cells will also be counted but because they are so few in number this does not significantly affect RBC coun
Explain what the function of a haemoglobin concentration (Hb) test is in a FBC
haemoglobin concentration (Hb) test is in a FBC
The haemoglobin concentration refers to the amount of haemoglobin in blood (g/L). It’s determined by lysis of red cells followed by conversion of haemoglobin to a stable form and spectrophotometry.
Turbidity of plasma can affect the Hb measurement
(overestimate)
In vitro haemolysis will reduce Hb
Explain what the function of a haematocrit (HCT) test is in a FBC
The hematocrit test gives the fraction of whole blood volume that consists of red blood cells.
This is done by multiplying the average red cell size (the mean cell volume (MCV)) by the number of red cells per litre to give the Haematocrit.
Explain what the function of a Mean cell volume (MCV) test is in a FBC
The MCV is an average volume of red cells measured in femtolitres (10-15 litres) and measured automatically by modern analysers (the amount of light or electric current impeded is proportional to the size of the cell).
This figure is useful in determining whether an anaemia is microcytic or macrocytic.
Explain what the function of a Mean Cell Haemoglobin (MCH) test is in a FBC
The MCH is the average amount of haemoglobin protein (measured in pg (10-15 Kg)) in an individual red blood cell.
It’s calculated 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 (reduces in iron deficiency, normal or increased in macrocyclic anamias)
Explain what the function of a Platelet Count test is in a FBC
The platelet count is a test used to measure the amount of platelets present in the blood.
Its determined by automated cell counting (interruption of a beam of light or electrical current as a line of single cells flow through a narrow tube).
As platelets are much smaller than red or white cells they can easily be distinguished from these by the analyser because the produce a much smaller signal.
First explain what reticulocytes are, then explain what the function of a Reticulocyte test is in a FBC and how this is carried out
- Reticulocytes are immature red blood cells i.e. the red cells which have just been released from the bone marrow into the blood.
- Reticulocytes are counted using special stains or fluorescent dyes which bind to ribosomal RNA (rRNA is not present in more mature red cells).
- The reticulocyte count is a very useful test in evaluating different kinds of anaemia.
- Increased: haemolytic anaemia, recent blood loos
- Reduced: defificney ir bone marrow failure
What is a blood film?
A blood film is also known as a peripheral blood smear.
Its a stained smear of a drop of blood that, when viewed through a microscope, produces additional morphologic information about the blood cells.
How is a blood film carried out?
It is made by placing a drop of blood at one end of the slide which is then thinly dispersed using a spreader slide to obtain a monolayer of cells which can be easily viewed under the microscope.
The sample is air dried and then fixed in methanol before staining to distinguish different cell types.
Whats the function of a blood film?
They’re used to look at cell morphology (structure).
Blood films are most commonly used to assess causes of low or high counts (RBC/WBC or platelets) and are also used to look for blood parasites (e.g. malaria and filariasis) or to check for abnormalities such as sickle cell anaemia, spherocytosis and thrombotic thrombocytopenic purpura (TTP).
Give the name for the following conditions:
- Increase in red blood cells
- Increases in white blood cells
- Increase in lymphocytes
- Increase in monocytes
- Increase in neutrophils
- Increase in eosinophils
- Increase in basophils
- Increase in platelets
- Increase in all blood cell types
- Polycythaemia or Erythrocytosis
- Leucocytosis
- Lymphocytosis
- Monocytosis
- Neutrophilia
- Eosinophilia
- Basophilia
- Thrombocytosis/thrombocythaemia
- Panmyelosis
Give the name for the following conditions
- Decrease in RBCs
- Decrease in WBCs
- Decrease in lymphocytes
- Decrease in monocytes
- Decrease in neutrophils
- Decrease in eosinophils
- Decrease in basophils
- Decrease in platelets
- Decrease in all blood cell types
- Anaemia
- Leucopenia
- Lymphocytopenia
- Monocytopenia
- Neutropenia
- Eosinopenia
- Basopenia
- Thrombocytopenia
- Pancytopenia
Explain the importance of using EDTA for FBC and the function of this substance
Blood samples for FBC must always be placed in a tube containing EDTA (ethylenediaminetetraacetic acid) 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.
What is meant by an abnormal result
Results outside the normal range (includes 95% of healthy population)
Give the factors that can affect normal range
Normal range changes with
- Age
- Sex
- Ethnicity
- Co-morbidities
Give the different errors at
What can cause errors in pathological results
Specimen collection:mix up, wrong bottle, pooling samples
Delivery of specimen to lab: delayed, wrong deiliveru method
Specimen analysis: mix up, incorrect clinical details, wrong test technical error
Responsive action: result not reviwed, reflex tests not carried out
What is spectrophotometry
a method to measure how much a chemical substance absorbs light by measuring the intensity of light as a beam of light passes through sample solution
Amount of light absorbed to the amount of absorbent compound within (measures Hb)
Uses a hypotonic solution to lose cells, appropriate light wavelength and a calibration curve to determine concentration
What is flow cytometry
technique to assess size, granularity, and protein expression (immunophenotype) of individual cells
Hydrodynamic focusing, counting the impedance cause by a cell as it passes through a light beam
More forward scatter= the bigger the size
How do you interpret a flow cytometry
Forward scatter= size
Side scatter = mono/polymorphonuclear, intracellular complexity
How does the blood composition of polycthemia and anemia compare to normal blood
Anemia: decreased hematocrit% and high plasma
Poly: elevated hematocrit and low plasma
What is packed cell volume (PCV)?
Proportion of blood that is made up of red blood cells (centrifuged bloods allows visual)
Used to asses anemia but more often polycythemia (reduced via drug treatment)
What is the red cell distribution width (RDW)?
Variations in the size of the red blood cells
If increased= anisocytosis
Helps to assess causes of anaemia:
Increased in iron deficiency (the first parameter to rise as iron stores fall)
Usually normal in thalassaemia trait.
Increased following transfusion
What is myeloperoxidase activity?
An indication of a granulocyte
When would a sample be flagged as requiring a blood film
Significant results outside the normal range
Significant change within a normal range
Analyser thinks there are abnormal cells
What does microcytic, macrocyclic, hypochromic and hyperchromic mean
Small rbc
Big rbc
Pale and less Hb
Dense more Hb in a given volume
What are common inclusion in erythrocytes
Howell jolly bodies- dna nuclear fragments
basophilin stippling - rna inclusions in cells
Pappenheimer bodies- iron inclusions
Heinz bodies - denatured Hb
Hb h inclusions- golf ball cells
In an iron deficiency what could you expect the reticulocyte and reticulocyte Hb content counts to be
Both low
Reticulocyte May be reduced for anaemia
What is spherocytosis?
- an auto-hemolytic anemia in which red blood cells are produced with a sphere-shape rather than a bi-concave disc
- red blood cell breakdown is increased because the spleen mistakes them for damaged erythrocytes
What type of cells will be present in a b12 deficiencies
Macrocytes, tear drop poilocytes, basophilic stipping and Howell jolly bodies
In a full blood count, what will be present in a vitamin b12 deficiency
Decrease: Hb, reticulocyte count and red cell count
Increased: red cell distibutuon width, mean cell Hb
What is important to consider about platelets in samples
If any clots in the sample the platelet count will be reduced due to platelet clumping
What can be seen in RCC in different types of microcytic anaemia?
reduced in iron deficiency anaemia
increased in thalassemia trait
What can be seen in RCC in polycythaemia?
Erythrocytosis: if RCC elevated, more likely to be a true
polycythaemia
Spurious polycythaemia caused by decreased plasma volume, RCC won’t be increased
How are individual types of WBCs counted ie neutrophils, basophils etc?
Automated blood analysers however if abnormal cells present u have to do it manually on blood film.
describe Mean cell haemoglobin concentration
Mean concentration of Hb in RBC (Hb/MCV x
RCC)
One of least useful parameters:
increased if spherocytosis.
Most useful in laboratory in the identification of
cold agglutinins (e.g. viral/ mycoplasma
infections etc.)
