6 - Full Blood Count Flashcards
How are blood result ranges derived and how do they decide what is considered normal?
- Normal range includes 95% of healthy population. 2.5% normal values above and below the range
- Normal depends on age, sex, ethnicity, comorbities
- Just because a result is normal, doesn’t mean it is normal for the patient and vice versa
How do you interpret if a blood result is abnormal?
- See if within the range
- Use previous FBC’s to compare with
- Diseases that can cause change
What are some errors in pathology results?
- Mix up in labelling
- Wrong bottle
- Blood pooling
- Cloting in tube
- Specimen delayed delivery
- Test variability due to technical error
- Wrong test ordered
What blood sample pot should be used for a FBC?
- Pink top EDTA and mixed
- EDTA chelates calcium ions and acts as anti-coagulant as if clotting cannot analyse
How is the white blood cell count carried out?
- Automated cell counting by interuption of beam of light
- After red blood cells have been lysed
How is the red blood cell count carried out?
- Same as white blood cell count but without lysis
- White blood cells will also be counted but doesn’t matter as there are only a small number of them
How is the haemoglobin concentration measured?
Lysis of red blood cells, conversion of haemoglobin to stable form and spectrophotometry. (g/L)
If doing a UE analysis why should you never pour blood from pink top to the yellow top?
The k+ salt from EDTA would give really high K+ reading
How is haematocrit measured? (HCT)
- Previously = centrifuge and height of red cell fraction with height of total blood (packed cell volume)
- Now: MCV x red cells per litre
How is mean cell (corpuscular) volume measured? (MCV)
- Amount of light or electrical current impeded is proportional to size
- Helps determine if anaemia micro or macrocytic
- Measured in femolitres 10-15
What is the word used to describe a high blood cell count in all areas?
Panmyelosis
How is mean cell Hb measured? (MCH)
Dividing haemoglobin concentration in a given volume, by the number of red cells in that volume
Measure in pg (10-15 kg)
How is platelet count measured?
Same principle as white and red blood cells but because much smaller they can be distinguished
How is the reticulocyte count measured?
- Stain or fluorescent dye added to bind to ribosomal RNA and can then be counted
- Useful for evalutating anaemias
How are different white blood cells counted individually?
- Differential white blood cell count
- Analysers can recognise the five different types
- If abnormal cell recognised it is neccessary to count manually on blood film
How is a blood film produced and when is a blood sample referred for one of these?
- Drop of blood at one end of slide, which is thinly dispersed to form a monolayer.
- Sample air dried, fixed in methanol and stained
- Useful for assessing high and low counts, blood parasites, blood abnormalities like sickle cell, spherocytosis and TTP
Explain what the following terms mean and what the red blood cells would look like on a blood film.
Explain what the following terms mean and what the red blood cells would look like on a blood film.
How do you lower a high Hct result?
- Venesection
- Drug treatment
Why are some Hb levels on blood tests invalid?
- Clotted sample will reduce Hb
- Turbidity of plasma can affect Hb measurement
- Dehydration/diuretics can lower plasma volume
- Acute bleed
What happens to RBC during thalassemia trait and anaemia iron deficiency?
Both are causes of microcytic anaemia
Why might the mean cell volume be low or high?
What is the relevance of RDW? (red cell distribution width)
- If increase = anisocytosis
- Increase in iron deficiency and following transfusion
- Normal in thalassemia trait
What does mean cell haemoglobin concentration tell you? (MCH)
Hb/MCV x RCC
- Reduced if hypochromic
- Increased in spherocytosis
Why might reticulocyte count be increased or decreased?
What is dimorphic and polychromasia on a blood film?
What would a patients blood results show if they had malaria?
- Decreased Hb and platelets
What are some inclusions in red blood cells and what are they caused by?
What would a blood test result show in an iron deficiency?
- Decreased Hb, MCV, MCH, MCHC
- Low/normal reticulocyte
- Hypochromic, microcytic, target cells, pencil cells all on blood film
What blood results would you expect from a patient with hereditary spherocytosis?
What would you see on a blood film with iron deficiency?
- Oval macrocytes
- Tear drop poikilocytes
- Basophilic stippling
- Howell-Jolly bodies
- Hypersegmented neutrophil
- Granulocytic precursors circulating
What is the most frequent abnormal parameter of a full blood count and why?
- Platelets as they are very reactive
- Reduced in clotted blood so use green tube with citrate
Why can sickle cell anaemia lead to joint and bone pain?
- Vasoocclusive episodes leading to ischemia
What is prophylatic laproscopic cholecystectomy and when is it carried out?
- Removal of gall bladder
- Prevents gall stones forming due to excess haemolysis and billirubin
- Can be done in haemolytic blood disorders, e.g sickle cell
What is acute chest syndrome and how is it treated?
- Vasoocclusive crisis in the pulmonary vasculature, mainly in sickle cell anaemia
- Exchange transfusion and broad spectrum antibiotics
Why might you have thrombocytopenia after a blood transfusion?
- Dilution of platelets as no platelets in stored blood
What is immune thrombocytopenic purpura?
- Issue where autoantibodies against platelet surface antigen
