2 - Deciding what is normal and interpreting blood count

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

Does haemoglobin show a Gausian/normal curve?

Answer 4

yes

Question 5

Does white blood cells show a Gausian/normal curve?

Answer 5

no

Question 6

To what power and units is WBC measured in?

Answer 6

10^9/L

Question 7

To what power and units is RBC measured in?

Answer 7

10^12/L

Question 8

To what power and units is Hb measured in?

Answer 8

g/L (g/dL)

Question 9

To what power and units is packed cell volume measured in?

Answer 9

no units (just a number)

Question 10

What is the difference between packed cell volume and haematocrit?

Answer 10

packed cell volume is not produced from centrifugation

Question 11

What unit is MCV measured in?

Answer 11

Femtolitres (10^-15 L)

Question 12

What unit is MCH measured in?

Answer 12

Picograms (10^-12 g)

Question 13

What unit is MCHC measured in?

Answer 13

g/L

Question 14

To what power and units is platelet count measured in?

Answer 14

10^9/L

Question 15

What is a caveat?

Answer 15

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

Question 16

Define MCV

Answer 16

(mean cell volume) the average size of a red cell

Question 17

Define MCH

How is it calculated?

Answer 17

(mean cell haemoglobin) average amount of Hb in a red cell

Hb/RBC

Question 18

Define MCHC

How is it calculated?

Answer 18

(mean cell haemoglobin concentration)
average Hb conc in a red cell

Hb/Hct

Question 19

What is RDW and what is it a measure of?

Answer 19

red cell distribution width

a measure of anisocytosis

Question 20

What is used as an anticoagulant and is coated in tube for blood collection?

Answer 20

EDTA

Question 21

How is Hb measured?

Answer 21

spectrophotometer

Question 22

How is haemtocrit measured?

Answer 22

microhaematocrit centrifugation
or
multiplying the red cell number by MCV

Question 23

How is MCV calculated?

Answer 23

light scattering or interruptions of an electrical field
or
dividing total volume of RBCs by the number of RBCs

Question 24

Describe the MCH and MCHC in someone with iron deficiency

Answer 24

MCH = reduced
MCHC = low

Question 25

Describe the MCH and MCHC in someone with red cell fragmentation

Answer 25

``` MCH = low MCHC = normal ```

Question 26

How is MCHC measured?

Answer 26

electronically on the basis of light scattering

Question 27

What is polycythaemia? | Which parameters are increased?

Answer 27

elevated number of red cells | Hb, RBC and Hct are increased

Question 28

What other cause is there of psuedopolycythaemia?

Answer 28

decreased plasma volume

Question 29

What are the causes of polycythaemia?

Answer 29

- 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)

Question 30

What are the signs of polycythaemia secondary to hypoxia?

Answer 30

finger clubbing and cyanosis

Question 31

What are the signs and symptoms of polycythaemia vera?

Answer 31

- hyper viscosity (thick blood) - can lead to vascular obstruction - very red hands and peripheral gangrene