Interpreting blood counts Flashcards
What is a reference range?
A set of values used by a health professional to interpret a set of blood test results
How is a reference range derived?
Derived from a carefully derived reference population, e.g. children 5-10yrs
Samples collected from healthy volunteers with defined characteristics
Analysed by instruments and techniques
Data analysed by appropriate technique
If data follow a normal (Gaussian) distribution, you can determine normal by taking 2 SDs on either side
This includes 95% of the data
How is a normal range derived?
Vague
Represents people that live in local area and come to hospital
Collect data from vast numbers of lab tests
95% predictive value - set of values 95% of the normal population fall within
What are the caveats of a reference range?
Not all results outside the RR are abnormal
Not all results within RR are normal
May be some overlap in results achieved by sick people and healthy people
What range can be more meaningful than a 95% reference range?
Health-related range
What factors can affect ‘normal’?
Age Gender Ethnic origin Physiological status (pregnant?) Altitude Nutritional status (majority of population malnourished?) Smoking Alcohol
What is polycythaemia?
Too many red cells in circulation
How can you diagnose polycythaemia from a FBC?
Increased Hb, RBC, Hct compared with normal subjects of same age and gender
How do you calculate mean cell haemoglobin?
MCH = Hb/RBC
How do you calculate mean cell haemoglobin concentration?
MCHC = Hb/Hct
What is MCH?
Mean cell haemoglobin
Absolute amount of haemoglobin in individual red cell
What is MCHC?
Mean cell haemoglobin concentration
Concentration of haemoglobin in cell
What is MCHC linked to?
Shape of the red cell
