S3 Interpreting Full Blood Count Flashcards
How is the normal range of results calculated?
By running tests on a group of healthy individuals (about 30) and find the mean
What factors result in normal range changes?
Age, sex, ethnicity and comorbidities
What do you do do if you have an abnormal or unexpected result?
Repeat the test
Interpret abnormal results in terms of clinical context and their previous full blood count (FBC) if known
When can errors in pathology results occur?
- Specimen collection
- Delivery of specimen to laboratory
- Specimen analysis and result reporting
- Responsive action
What errors can occur in specimen collection?
- specimen mix up
- wrong blood in tube (WBIT)
- wrong bottle
- pooling samples
- poor technique
What is pooling samples?
Mixing two samples together to get the desired amount of blood in a sample tube
What errors can occur in delivery of the specimen to the laboratory?
- specimen delayed/not delivered (sample can become to old to examine)
- wrong delivery method (e.g. not in ice when it should be)
What errors can occur in specimen analysis and result reporting?
- specimen mix up (booking in)
- incorrect clinical details
- wrong test requested/performed
- inherent test variability (as the analysers aren’t completely accurate)
- technical error
What errors can occur in the responsive action?
- result not reviewed
- reflex tests not carried out
- right result applied to wrong patient
What is the FBC analyser like?
- a closed system
- easy to maintain
- able to cope with high numbers of samples
Why do you use a pink top EDTA sample?
To stop blood coagulation
What are concurrent parameters in a FBC?
- red cells - indices, number (RCC), haemoglobin
- platelets - count, size
- white cells - count, full differential
What are the different FBC analyser techniques?
- spectrophotometry
- flow cytometry
- flow cytometry differential
What is a spectrophotometry?
The amount of light absorbed by the sample is proportional to the amount of absorbent compound within it (used to measure Hb)
- Uses a hypotonic solution to lyse cells
- Use light of an appropriate wavelength
- Use a calibration curve to determine the sample conc
What is a flow cytometry?
Used for counting number of cells and their size
- A single file line of cells passes through the machine
- The cells pass through a light beam (they interrupt the beam)
- This interruption is recorded - used to determine number of cells
- The scatter pattern determines the size of the cell e.g. the more forward scatter, the bigger the cell
What is a flow cytometry differential?
Measures scatter
- forward scatter determines size
- side scatter determines whether the cell is mono/polynucleated and its intracellular complexity e.g. granules
The myeloperoxidase activity is also measured - this is linked to granulocytes
What is the packed cell volume (PCV/Hct) (L/L)? What is it used to assess?
Proportion of blood that is made up of RBCs
Assesses: anaemia or polycythemia - lower PCV/Hct in polycythemia (more RBCs)
What are haemoglobin levels (g/L) used to assess? What are the reference ranges?
Assesses: acute bleed, haemolytic, bone marrow disorders
- less than 135 in adult men
- less than 115 in adult women
- less than 110 in children (3-12)
- less than 150 in newborns
What can affect the Hb measurement and cause an overestimate? What will reduce Hb?
Turbidity
In vitro haemolysis/clotted sample
What is the red cell count (RCC) (x10^12/L)? What is it used to assess?
The number of RBCs in a given volume of blood
Assesses: anaemia (reduced in iron deficient anaemia, increased in thalassemia) and erythrocytosis (increased)
What is the mean cell volume (MCV) (fL)? What is it used to assess?
The mean RBC size, measured using the amount of light scattered as they pass in a single file past a laser (flow cytometry)
Assesses: used to screen the cause of anaemia e.g. if high could be haemolytic anaemia, hypothyroidism or myeloma, if low could be iron deficiency anaemia, thalassaemia or lead poisoning
What is the mean cell Hb (MCH) (pg)? What is it used to assess?
Average measure of the amount of Hb in each RBC (Hb/RCC)
Assesses: anaemia (lower in iron deficiency, normal/increased in macrocytic anaemias)
What is the mean cell Hb concentration (MCHC) (g/L)?
Is this useful?
The mean concentration of Hb in RBC (Hb/MCV x RCC)
No
What is red cell distribution width (RDW)? What does it mean if it’s increased? What is it used to assess?
Variation in the size of the RBC
Ansiocytosis (variation in RBC size)
Assesses: the cause of anaemia - increased in iron deficiency, normal in thalassaemia, increased after transfusion
What is the reticulocyte count (x10^9/L)? In which cases is this increased or decreased?
Measurement of the number of young erythrocytes
They’re identified using size and RNA content
Increased in haemolytic anaemia, recent blood loss or response to erythropoietin
Decreased in bone marrow failure
When is a sample flagged for needing a blood film?
- if significant result is outside the normal range
- if there is a significant change within the normal range
- if analyser thinks there are abnormal cells (e.g. immature cells or unable to identify cells)
How do you do a blood film?
- A small drop of blood is spread onto a glass slide (layer is 1 cell thick)
- The sample is fixed with methanol
- The sample is stained to enable visualisation under a microscope
What does microcytic (measure with MCV) mean?
Small RBCs
What does macrocytic (measure with MCV) mean?
Large RBCs
What does hypochromic (measure with MCH) mean?
Pale, less Hb
What does hyperchromic (measure wit h MCH) mean?
Dense, more Hb in a given volume
What is ansiocytosis?
Variation in size
What is dimorphism?
Two distinct populations of red cells
What is poikilocytosis?
Abnormally shaped RBC
What is spherocytosis?
Spherical RBC
What is elliptocytosis?
Elliptical RBC
What are irregularly contracted cells?
Small dense RBC but not as regular in shape as spherocytes
What are echinocytes, acanthocytes and keratocytes?
Spiculated cells
What are sickle cells?
Crescent or sickle shaped cells seen in sickle cell disease
What are target cells?
RBC with a dark area in the middle of the area of central pallor (paleness)
What is schistocytes?
Red cell fragments
What is polychromasia?
Many colours - reticulocytes
What are Howell-Jolly bodies?
DNA/nuclear fragments
What is basophilic stippling?
RNA inclusions in cells
What are Pappenheimer bodies?
Iron inclusions in cells
What are Heinz bodies?
Denatured Hb
What are Hb H inclusions?
‘Golf-ball cells’ - Hb H (stains blue)
What are the Hb, MCV, MCH, MCHC and RDW in iron deficiency?
- Hb, MCV, MCH, MCHC are decreased
* RDW is increased
What is the reticulocyte count and reticulocyte Hb content (CHr) in iron deficiency?
Reticulocyte count is low to normal
CHr is low
What do cells look like on a blood film for iron deficiency?
Hypochromic
Microcytic
Pencil cells
A few target cells
What are the levels of Hb, MCV, RDW, MCH, MCHC and reticulocyte count in spherocytosis?
Hb - normal or increased MCV - normal RDW - increased MCH - normal MCHC - increased Reticulocyte count - increased
What are the levels of Hb, RCC, MCV*, RDW, MCH, MCHC, Hct/PCV and reticulocyte count in vitamins B12 deficiency?
Hb - decreased RCC - decreased MCV* - increased RDW - increased MCH - increased MCHC - normal Hct/PCV - decreased (as there’s a lower RCC) Reticulocyte count - decreased
Give 3 examples when WBCs increased?
- infection
- inflammation
- drugs
What can nucleated RBCs be counted as by the analyser?
As white cells
What is the most frequent parameter that varies from normal?
Platelet number
Will clots in sample increase or decrease platelet number?
Decrease
