Haem 2 Flashcards
Define reference range
A reference range is derived from a carefully defined reference population
What is a normal/gaussian distribution
determining the mean and standard deviation and taking mean ± 2SD as the 95% range
Data with a different distribution must be analysed by an alternative method
t/f Hb shows normal distribution
T
t.f. wbc shows a normal distribution
F
Unit for WBC, RBC, Hb, PCV and Hct
PCV=Hct
(× 109/l) (× 1012/l) (g/l) (l/l) (l/l) i.e. litre of cells per litre of blood (expressed as decimal) so basically fraction of blood made of cells
What is MCV, MCH, MCHC and platelet count measured in
fl, pg, g/l, X109/l
How does Hb change with altitude
6,500 ft Hb 0.8-1 g/l
10,000 ft 20 g/l
13,000 ft 35 g/l
How are WBC, RBC and platelet count determined
enumerating electronic impulses generated when cells flow between a light source and a sensor or when cells flow through an electrical field
How is Hb measured
measured in a spectrometer, by converting haemoglobin to a stable form (used to involve cyanide) and measuring light absorption at a specific wave length
Now measured by an automated instrument but the principle is the same
Absorption range of Hb
Hugh at 400, down at 500, up again just other then down again. Little after 700
How is PCV (=HCt) calculated
Centrifuging blood sample
How is MCV calulated
Hct (*1000)/RBC…. Now determined indirectly by light scattering or by interruption of an electrical field
Differentiate normal range and health-related range
A result within the 95% range determined from apparently healthy people may still be bad for your health
e.g serum lipids
How to caculate MCH
Hb/RBC
The amount of haemoglobin in a given volume of blood divided by the number of red cells in the same volume
How to calculate MCHC
The amount of haemoglobin in a given volume of blood divided by the proportion of the sample represented by the red cells.
Hb/PCV
Difference between MCH and MCHC
If there is a small cell, and there is a lower concentration of haemoglobin than a large cell, it will have low MCH and MCHC.
If there are small cells but the concentration is the same in a small cell as a large cell, the MCH will still be low but the MCHC will be normal….
The MCH is the absolute amount of haemoglobin in an individual red cell
The MCHC is the concentration of haemoglobin in a red cell
Basically… with MCH, you’re just diving Hb by RBC, so working out average amount of Hb in each red blood cell
In MCHC you divide Hb/Hct… Hct will be smaller or bigger if the average cell size is smaller or bigger, whereas RBC is just the number, not the size….
so MCHC takes into account the volume of the red blood cell… so it gives a concentration of Hb rather than just an amount of Hb per cell
What is the MCH parallel with in microcytic and macrocytic anaemia
Parallel to MCV
Define polycythaemia
means ‘many cells’ but it refers specifically to too many red cells in the circulation
The Hb, RBC and PCV/Hct are all increased compared with normal subjects of the same age and gender
Pseudo polycythaemia
Reduced blood volume
True polycythaemia
Increase in total volume of red cells in the circulation
What could cause true polycythaemia
Blood doping or overtransfusion
Appropriately increased erythropoietin
Inappropriate erythropoietin synthesis or use
Independent of erythropoietin
How would a small cell where the blood has reduced MCH but a normal MCHC look
It would be a small cell but normal colour
How would a small cell with where the blood has reduced MCH but a reduced MCHC look
Hypochromic
What is MCHC related to
MCHC: The colour of the cell
MCH: related to the size
t/f Hb, RBC and Hct are higher in the neonate than at other times of life
T
t/f Hb, RBC and Hct are higher in children than in adults
F
T/F Hb, RBC and Hct are lower in women than in men
t
When could polycythaemia result from the action of erythropoietin that is appropriately elevated?
In Tibet, why doesn’t every one have polycythaemia!?
In altitude (However residents of the Tibetan plateau have a 85% prevalence of a mutation that reduces the erythropoietin production in response to hypoxia to avoid polycythaemia)
Sign of polycythaemia
Clubbing
Examples of inapporpriate increase in erythropoietin
erythropoietin is inappropriately administered to haematologically normal subjects
OR
when a renal or other tumour inappropriately secretes erythropoietin
Example of polycythaemia independent of erythropoietn
intrinsic bone marrow disorder called polycythaemia vera It is classified as a myeloproliferative neoplasm
What happens in polycythaemia vera
‘thick blood’– more technically known as hyperviscosity
This can lead to vascular obstruction
How to interpret FBC for cause of polycythaemia:
- of a breathless cyanosed patient
- An abdominal mass
- Splenomegaly
A breathless cyanosed patient ‒ probably due to hypoxia
it could be carcinoma of the kidney
a pointer to polycythaemia vera (blocking supply to spleen)
Treatment for polycythaemia
If there is no physiological need for a high haemoglobin, or if hyperviscosity is extreme, blood can be removed to thin the blood
If there is intrinsic bone marrow disease, drugs can be used to reduce bone marrow production of red cells (e.g polycythaemia vera)
What might happen to the MCHC and the MCH in hereditary spherocytosis
MCHC could increase, whilst MCH could remain normal
When might MCHC be reduced
severe thalassaemia or Fe deficiency anaemia
