2 - Deciding what is normal and interpreting blood count Flashcards
State some factors that affect what is ‘normal’.
Age Gender Ethnic origin Physiological status Altitude Nutritional status Cigarette smoking Alcohol intake
What is the difference between a reference range and a normal range?
Reference Range = derived from a carefully defined reference population e.g. children 5-10 years
Normal Range = much vaguer – it should represent the people that live in the local area and come to the hospital
How is a reference range determined?
Samples are collected from healthy volunteers with defined characteristics.
The data is analysed by appropriate techniques.
If the data follows a normal (Gausian) distribution, you can determine what is normal by taking the mean and taking 2 standard deviations on either side.
Between the 2 SDs on either side, you will have 95% of the data.
Does haemoglobin show a Gausian/normal curve?
yes
Does white blood cells show a Gausian/normal curve?
no
To what power and units is WBC measured in?
10^9/L
To what power and units is RBC measured in?
10^12/L
To what power and units is Hb measured in?
g/L (g/dL)
To what power and units is packed cell volume measured in?
no units (just a number)
What is the difference between packed cell volume and haematocrit?
packed cell volume is not produced from centrifugation
What unit is MCV measured in?
Femtolitres (10^-15 L)
What unit is MCH measured in?
Picograms (10^-12 g)
What unit is MCHC measured in?
g/L
To what power and units is platelet count measured in?
10^9/L
What is a caveat?
a warning or proviso of specific stipulations, conditions, or limitations
a health related range, rather than reference ranges where people outside are cut off and said to be abnormal
Define MCV
(mean cell volume) the average size of a red cell
Define MCH
How is it calculated?
(mean cell haemoglobin) average amount of Hb in a red cell
Hb/RBC
Define MCHC
How is it calculated?
(mean cell haemoglobin concentration)
average Hb conc in a red cell
Hb/Hct
What is RDW and what is it a measure of?
red cell distribution width
a measure of anisocytosis
What is used as an anticoagulant and is coated in tube for blood collection?
EDTA
How is Hb measured?
spectrophotometer
How is haemtocrit measured?
microhaematocrit centrifugation
or
multiplying the red cell number by MCV
How is MCV calculated?
light scattering or interruptions of an electrical field
or
dividing total volume of RBCs by the number of RBCs
Describe the MCH and MCHC in someone with iron deficiency
MCH = reduced MCHC = low
Describe the MCH and MCHC in someone with red cell fragmentation
MCH = low MCHC = normal
How is MCHC measured?
electronically on the basis of light scattering
What is polycythaemia?
Which parameters are increased?
elevated number of red cells
Hb, RBC and Hct are increased
What other cause is there of psuedopolycythaemia?
decreased plasma volume
What are the causes of polycythaemia?
- blood doping/illicit erythropoietin (blood is transfused to increase performance)
- medical negligence (administered too much blood)
- high levels of erythropoietin (this can be as a result of hypoxia e.g. high altitude)
- polycythaemia vera (increased erythropoiesis)
What are the signs of polycythaemia secondary to hypoxia?
finger clubbing and cyanosis
What are the signs and symptoms of polycythaemia vera?
- hyper viscosity (thick blood)
- can lead to vascular obstruction
- very red hands and peripheral gangrene
