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
