Haem 2 - Deciding what is normal and interpreting blood counts - Polycythaemia as an example

Question 1

How is a normal or reference range determined

Answer 1

Reference range = derived from carefully defined reference population (samples from healthy volunteers with defined characteristics)

Normal range - vaguer concept

Question 2

What does RDW on a full blood count mean?

Answer 2

RBC distribution width (measure of anisocytosis)

Question 3

Packed cell volume (PCV) and haematocrit (Act) are measured how?

Answer 3

Centrifuging

Question 4

Mean cell volume is calculated how?

Answer 4

PCV / RBC

Question 5

MCH is calculated how?

Answer 5

Hb / RBC

Question 6

MCHC is calculated how?

Answer 6

Hb / PCV

Question 7

What is the difference between MCH and MCHC

Answer 7

MCH = absolute Hb present

MCHC = is a measure of concentration (so is relative to size of cell)

Question 8

When might MCHC be low? High?

Answer 8

Low MCHC = thalassaemia

High = spherocytosis

Question 9

Hypochromia correlates to which full blood count value?

Answer 9

MCHC

Question 10

What should we interpret first in a blood count

Answer 10

1. WBC and differential (look at absolute count not percentage)
2. Hb
3. MCV
4. Platelet count

Question 11

What does polycythaemia/erythrocytosis mean

Answer 11

Too many red cells in circulation

Increased Hb, RBC, PCV/Hct

Question 12

There are 2 forms of polycythaemia - pseudo and true. Describe each one

Answer 12

Pseudo polycythaemia = reduced plasma volume . Often caused by shock/dehydration, or chronic

True polycythaemia = increase in total volume of red cells in circulation

Question 13

What are the causes of true polycythaemia

Answer 13

1. Blood doping / overtransfusion
2. Appropriately increased erythropoietin
3. Inappropriate erythropoietin synthesis/use
4. Independent of erythropoietin

Question 14

Hb, RBC and Hct are highest at what period in life?

Answer 14

Neonates

Also children have lower Hb/RBC/Hct than adults and lower in women than men

Question 15

Cyanosis and clubbing indicate?

Answer 15

Hypoxia - meaning they probs have high erythropoietin

Question 16

What is polycythaemia vera

What can it lead to?

Answer 16

Intrinsic bone marrow disorder - inappropriately increased erythropoiesis that is independent of erythropoietin

It is classified as a myeloproliferative neoplasm

Polycythaemia vera can lead to very thick, viscous blood - causing vascular obstruction

Question 17

How is polycythaemia treated

Answer 17

Blood can be removed (if no physiological need for high Hb)

Or if intrinsic bone marrow disease (polycythaemia vera) - drugs given to reduce bone marrow production of red cells

Question 18

If the FBC clinical context shows polycythaemia and abdominal mass

Answer 18

Could be carcinoma of kidney