What is normal and interpreting blood counts?

Question 1

Why is normal hard to define?

Answer 1

The definition of ‘normal’ is variable and dependant on; age, gender, ethnic origin, physiological status (i.e. pregnancy), altitude, nutritional status and cigarette/alcohol intake

Question 2

What is reference range?

Answer 2

A range derived from a carefully defined reference population

Question 3

How is a reference range derived?

Answer 3

• These are derived by collecting samples from healthy volunteers with defined characteristics
• The volunteers are then analysed using the same instruments and techniques that will be used for patient samples – to ensure variables are kept to a minimum

Question 4

How are the reference ranges analysed?

Answer 4

Data with a normal (or Gaussian) distribution is analysed using mean and SD to determine the 95% range (mean ±2SDs) Data that does not have a normal distribution uses different techniques.

Question 5

What kind of distribution do Hb and WBCs show?

Answer 5

Hb shows a GAUSSIAN/NORMAL distribution

WBCs show a NON-NORMAL distribution

Question 6

Why must normality take into account the situation?

Answer 6

Not all results outside the reference range are abnormal as are not all results inside the reference range are normal – i.e. a man with a GI bleed with a normal Hb count is not normal for the situation.

Question 7

What is normal WBC?

Answer 7

30.4 * 10^9/L

Question 8

What is normal RBC?

Answer 8

4.75 * 10^12/L

Question 9

What is normal Hb?

Answer 9

15.4 g/dL

Question 10

What is normal MCH?

Answer 10

32.3 pg

Question 11

What is normal MCHC?

Answer 11

33.1 g/dL

Question 12

What is normal MCV?

Answer 12

98 fl

Question 13

What is normal platelet count?

Answer 13

215 * 10^9 /L

Question 14

What is MCH?

Answer 14

MCH is the absolute amount of Hb in an individual RBC.

Question 15

What is MCHC?

Answer 15

Concentration of the Hb in the RBC so changes with cell size while MCH won’t

Question 16

What happens in micro/macrocytic anaemias to MCH and MCV?

Answer 16

they tend to parallel

Question 17

How is RBC, WBC, platelet count taken?

Answer 17

Initially counted visually on a slide, now counted by machines by enumerating electronic impulses generated when cells flow between a light source and a sensor (or through an electrical field

Question 18

How is Hb measured?

Answer 18

Initially measured in a spectrometer (by converting Hb to a stable form and measuring light absorption) and principle is still the same, the process is now automatic.

Question 19

How are PCV and Hct measured?

Answer 19

Initially measured by centrifuging a blood sample.

Question 20

What is MCV?

How is it calculated and measured?

Answer 20

 Total volume of RBCs in a sample divided by the total number of RBCs in a sample.
PCV/RBC

Now determined indirectly by – light scattering OR interruption in an electrical field

Question 21

What is the formula for MCH?

Answer 21

Amount of Hb in a given volume of blood divided by the number of RBCs in the same volume

Hb/RBC

Question 22

What is the formula for MCHC?

Answer 22

Amount of Hb in a volume of blood divided by the proportion of sample represented by RBCs.

Hb/PCV, Hb/Hct

Question 23

What could high MCHC suggest?

Answer 23

High MCHC could indicate irregularly contracted cells of spheroidal cells

Question 24

How should blood counts be interpreted?

Answer 24

1. Is there leucocytosis or leucopenia?
   a. If so, why?
   b. Which cell line is abnormal? Any clinical history clues?
2. Is there anaemia?
   a. If so, is there any clues in the blood count?
   b. Are the cells large or small? Any clinical history clues?
3. Is there thrombocytosis or thrombocytopenia?
   a. If so, is there any clues in the blood count?
   b. Any clinical history clues?

To begin interpretation, learn to interpret; WBCs and differentials (absolute count, not percentage), Hb, MCV, platelets count.
You may also need to look at a blood film – i.e. type of anaemia

Question 25

What is polycythaemia?

Answer 25

Too many RBCs in circulation.

Question 26

In polycythaemia what happens to Hb, RBC and Hct?

Answer 26

all increased

Question 27

How should the patient be examined for polycythaemia?

Answer 27

Clinical history & Physical examination – splenomegaly, abdominal mass or cyanosis could be relevant

Compare the above with the appropriate normal range

Question 28

How does the Hb, Hct and RBC vary between ages?

Answer 28

The Hb, RBC and Hct will all be higher in a neonate, lower in children than adults and lower in women than in men.

Question 29

What is pseudopolycythaemia?

Answer 29

The same symptoms of polycythaemia can be present but due to a decrease in plasma volume (so increase in concentration). I.E. burns draw plasma to the surface.

Question 30

What are the causes of pseudopolycythaemia?

Answer 30

Blood doping – adding blood to your own – too much blood

Medical negligence – i.e. gave too much blood in a transfusion. Can then give venesections (remove blood)

Erythropoietin:

1. Physiological high levels of erythropoietin – increased blood cell production in response to hypoxia at altitude.
2. Illicit erythropoietin – inappropriate administration to artificially raise RBC count.
3. Tumour erythropoietin – renal or ectopic tumour secretes erythropoietin.

Abnormal function of bone marrow – inappropriate increased erythropoiesis without erythropoietin.
This is called polycythaemia vera – classed as a myeloproliferative neoplasm.
This can lead to hyperviscous blood and vascular obstruction.

Question 31

How is polycythaemia treated?

Answer 31

Blood removal – venesection

Drugs – for intrinsic bone marrow disease, drugs can reduce production of RBCs in bone marrow

Question 32

What is important to consider when interpreting a FBC?

Answer 32

Always be aware of the clinical history – i.e. a young healthy athlete with polycythaemia is very suspicious but a breathless cyanosed patient has it probably due to hypoxia