Haematology 2 (deciding what Is Normal) Flashcards
What is the difference between MCH and MCHC ?
- MCH = Absolute amount of hb in an individual red cell
- MCHC = Conc of hb in a red cell
NOTE: microcytic + macrocyclic anaemia - MCH parallel MCV
What is the difference between pseudo polycythaemia and true polycythaemia
Pseudo = high hb/rbc/hct results from decrease in plasma volume
True = results from. Increase in no of circulating rbc
How is reference range determined ?
- Samples collected from healthy volunteers with defined characteristics
- They are analysed using instrument + techniques that will be used on patient samples
- The data is analysed by an appropriate technique
- data with normal distribution (e.g hb conc) = analysed by determining mean + 2S.D (which is taken as the 95% range)
- if not normally distributed (e.g wbc count) - diff method used for analysis
Note :
- not all results outside reference range = normal
- not all results within normal range = normal
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How is wbc / rbc / platelet count conducted nowadays?
Using automated machines
- they count the number of electrical impulses generated when cells flow between a light source and a sensor
Or when cells flow through an electric field
How is hb measured?
Initially: measured using spectrometer
Now: automated machine
both methods involve
- converting hb to a stable form
- then measure light absorption at specific wave length
How is hct and MCV and MCHC measured?
Initially (hct): centrifuging blood sample
Initially MCV: total volume of rbc/ no. of rbc in sample
Now (hct + MCV + MCHC) : light scattering
Or by interruption of an electrical field
What are 4 main causes of PSEUDO polycythaemia?
- Blood doping (in cyclists) / over transfusion
- high levels of erythropoietin that is appropriately elevated (e.g if smoker, or due to altitude)
- tumour (e.g renal) inappropriately secretes erythropoietin (too much erythropoietin)
- Independent of erythropoietin = polycythaemia Vera (intrinsic bone marrow disorder)—> leads to hyperviscosity —> vascular obstruction –> coronary/cerebral infarction
What is the effect of polycythaemia ?
- can lead to hyperviscosity of blood
- which in turn can lead to vascular obstruction
What is MCHC ?
Mean cell hb conc
- amount of hb in a given volume of blood / proportion of the sample represented by rbc
- I.e hb / hct
What can ‘normal’ be affected by ?
A G E P A N C A
Age Gender Ethnic origin Physiological status Altitude Nutritional status Cigarette smoking Alcohol intake
What is polycythaemia?
Polycythaemia = too many red cells in the circulation
- hb, rbc, hct are all increased
What is MHC ?
- mean cell hb
- amount of hb in a given volume of blood / no. Of rbc in the same volume
- I.e hb/rbc
What is the difference between reference range and normal range ?
- reference range = derives from carefully defined reference population
(healthy individuals) - normal range = vaguer concept
note:
- normal for one group of population might not be normal for others.
- e.g serum lipid levels in western countries tend to be higher
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