Deciding What Is Normal and Interpreting A Blood Count

Question 1

Reference range?

Answer 1

Range derived from a carefully defined reference population

Question 2

Normal range?

Answer 2

Normally in which 95% of population lies within - harder to define

Question 3

E.g. of the the limitations of a normal range?

Answer 3

e.g. altitude & [Hb]

The greater the altitude, the higher the [Hb] so hard to establish normal range

Question 4

How is the reference range determined/derived?

Answer 4

o samples are collected from healthy volunteers with defined characteristics

o these are analysed use the SAME instruments & techniques and the data is then analysed

Question 5

Another word for ‘Normal Distribution’?

Answer 5

Gaussian distribution

Question 6

Caveats in terms of the reference range?

Answer 6

Not all results outside the reference range OR within the normal range are ab/normal

SO a health-related range may be more useful than a 95% range

Question 7

Main things to see in a full blood count?

Answer 7

WBC (10^9/l)
RBC (10^12/l)
Hb (g/l)
Hct (ratio)
PCV (ratio)
MCV (fl)
MCH (pg)
MCHC (g/l)
Platelet count (10^9/l)

Question 8

How is WBC, RBC and platelet measures?

Answer 8

Before:
o counted visually via. microscope & diluted blood sample

After:
o counted in large automated instrument

Question 9

How is Hb measured?

Answer 9

Before:
o spectrometer via. converting Hb to a stable form

Now:
o automated instrument BUT principle is the saem

Question 10

How is PCV or Hct measured?

Answer 10

Centrifuging a blood sample

Question 11

MCV?

Answer 11

Before:
o Volume of RBCs in sample / Total no. of RBCs in sample

i.e. PCV/RBC

Now:
o indirectly by light scattering or interruption of an electrical field (e.g. larger cell = more scattering/interruption)

Question 12

MCH?

Answer 12

AMOUNT of Hb in a given volume of blood / NUMBER of RBCs in same volume

i.e. Hb / RBC

so absolute amount of Hb in an individual RBC

Question 13

MCHC?

Answer 13

AMOUNT of Hb in a given volume of blood / PROPORTION of sample represented by RBCs

i.e. Hb / Hct

so the concentration of Hb in the RBC

Question 14

What effects MCH?

Answer 14

In micro/macrocytic anaemias, MCH tends to PARALLEL the MCV

i.e. MCV rises = MCH rises vice versa.

Question 15

What effects MCHC?

Answer 15

Changes to the shrinkage OR growth of the cell (MCH will NOT be affected by this)

Question 16

What would HIGH MCHC show?

Answer 16

Hypochromia - could indicate irregularly contracted cells of spheroidal cells

Question 17

Steps to interpret a blood count?

Answer 17

1. Is there leucocytosis or leucopenia?
2. Is there anaemia?
3. Is there thrombocytosis or thrombocytopenia?

Question 18

What should be checked first when interpreting a blood count?

Answer 18

o WBC and differential
o Hb
o MCV
o Platelet count

Question 19

Define Polycythaemia?

Answer 19

Too MANY RBCs in circulation

Question 20

What happens during polycythaemia?

Answer 20

Hb, RBC and Hct/PCV are all INCREASED

compared with normal subjects of the same age/gender

Note: these are:
o higher in the neonate than other times of life
o lower in children than adults
o lower in women than men

Question 21

2 types of polycythaemia?

Answer 21

Pseudo

True

Question 22

Difference between pseudo and true polycythaemia?

Answer 22

Pseudo - REDUCED PLASMA volume (i.e. increased on [ ])

True - INCREASE in total volume of RBC in the circulation
o classed as a MYELOPROLIFERATIVE NEOPLASM (look at causes of polycythaemia)

Question 23

How do you evaluate polycythaemia?

Answer 23

1. Clinical history & physical examination (e.g. splenomegaly, abdo mass or cyanosis)
2. Compare with an appropriate normal range

Question 24

Causes of polycythaemia?

Answer 24

o Blood doping - addition of RBCs to own blood = too much blood

o Medical negligence - i.e. gave too much blood during transfusion (note need to look at weight as lighter people need less)
= can overcome by giving VENESECTIONS to remove excess blood

o High levels of erythropoietin - can be:
- PHYSIOLOGICAL high levels i.e. altitude or hypoxia

• ILLICIT i.e. inappropriately administered to artificially raise RBC count
• TUMOUR i.e. renal or ectopic tumour secreting erythropoietin

o Abnormal functioning of the bone marrow - inappropriate increase of ERYTHROPOIESIS WITHOUT erythropoietin = POLYCYATHAEMIA VERA

Question 25

What happens in PCV or Hct goes above 50%?

Answer 25

Blood viscosity INCREASES so disadvantageous as more prevalent towards HAs and strokes

Can be seen in Polycythaemia Vera

Question 26

Treatment for polycythaemia?

Answer 26

o Venesections (blood removal)

o Drugs - i.e. if have intrinsic bone marrow disease so can help reduce bone marrow production of RBCs

Question 27

How do you interpret a FBC?

Answer 27

Always see it in the context of clinical hisotry and physical findings!!

E.g.
o young healthy athlete shows polycythaemia = SUSPICIOUS

o breathless cyanosed patient = probably due to hypoxia

o abdominal mass = could be carcinoma of the kidney

o splenomegaly = pointed to polycythaemia vera