Deciding what is normal and interpreting blood counts

Question 1

State some factors that affect what is ‘normal’.

Answer 1

Age 
Gender 
Ethnic origin  
Physiological status  
Altitude 
Nutritional status  
Cigarette smoking  
Alcohol intake

Question 2

What is the difference between a reference range and a normal range?

Answer 2

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

Question 3

How is a reference range determined?

Answer 3

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.

Question 4

What unit is MCV measured in?

Answer 4

Femtolitres (10^-15L)

Question 5

What unit is MCH measured in?

Answer 5

Picograms (10^-12g)

Question 6

How are these parameters measured now?

Answer 6

It is determined indirectly by light scattering or by interruption of an electrical field