Haem 2 - Deciding what is normal and interpreting blood counts - Polycythaemia as an example Flashcards
How is a normal or reference range determined
Reference range = derived from carefully defined reference population (samples from healthy volunteers with defined characteristics)
Normal range - vaguer concept
What does RDW on a full blood count mean?
RBC distribution width (measure of anisocytosis)
Packed cell volume (PCV) and haematocrit (Act) are measured how?
Centrifuging
Mean cell volume is calculated how?
PCV / RBC
MCH is calculated how?
Hb / RBC
MCHC is calculated how?
Hb / PCV
What is the difference between MCH and MCHC
MCH = absolute Hb present
MCHC = is a measure of concentration (so is relative to size of cell)
When might MCHC be low? High?
Low MCHC = thalassaemia
High = spherocytosis
Hypochromia correlates to which full blood count value?
MCHC
What should we interpret first in a blood count
- WBC and differential (look at absolute count not percentage)
- Hb
- MCV
- Platelet count
What does polycythaemia/erythrocytosis mean
Too many red cells in circulation
Increased Hb, RBC, PCV/Hct
There are 2 forms of polycythaemia - pseudo and true. Describe each one
Pseudo polycythaemia = reduced plasma volume . Often caused by shock/dehydration, or chronic
True polycythaemia = increase in total volume of red cells in circulation
What are the causes of true polycythaemia
- Blood doping / overtransfusion
- Appropriately increased erythropoietin
- Inappropriate erythropoietin synthesis/use
- Independent of erythropoietin
Hb, RBC and Hct are highest at what period in life?
Neonates
Also children have lower Hb/RBC/Hct than adults and lower in women than men
Cyanosis and clubbing indicate?
Hypoxia - meaning they probs have high erythropoietin
What is polycythaemia vera
What can it lead to?
Intrinsic bone marrow disorder - inappropriately increased erythropoiesis that is independent of erythropoietin
It is classified as a myeloproliferative neoplasm
Polycythaemia vera can lead to very thick, viscous blood - causing vascular obstruction
How is polycythaemia treated
Blood can be removed (if no physiological need for high Hb)
Or if intrinsic bone marrow disease (polycythaemia vera) - drugs given to reduce bone marrow production of red cells
If the FBC clinical context shows polycythaemia and abdominal mass
Could be carcinoma of kidney
