Deciding what is normal and interpreting blood counts

Question 1

What is the difference between a reference range and a normal range?

Answer 1

Reference Range = derived from a carefully defined reference population e
Normal Range = much vaguer

Question 2

How is a reference range determined?

Answer 2

Samples are collected from healthy volunteers with defined characteristics.
The data is analysed by appropriate techniques and instrument.

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 3

What unit is MCV measured in?

Answer 3

Femtolitres, fL (10^-15L)

Question 4

What unit is MCH measured in?

Answer 4

Picograms, pg (10^-12g)

Question 5

How are these parameters measured now?

Answer 5

counted in large automated instruments, by enumerating electronic impulses generated when cells flow between a light source and a sensor or when cells flow through an electrical field

Question 6

units of WBC

Answer 6

white blood cell count in a given volume of blood (× 10^9/l)

Question 7

RBC units

Answer 7

RBC – red blood cell count in a given volume of blood (× 10^12/l)

Question 8

Hb units

Answer 8

g/L

Question 9

PCV units / Hct units

Answer 9

PCV=Hct same thing.

L/L (litres of RBC per litres of blood)

Question 10

MCHC units

Answer 10

g/L

Question 11

platelet units

Answer 11

(× 10^9/l) , same as WBC

Question 12

what parameter does staining correlate with

Answer 12

MCHC (concentration of Hb per RBC)

Question 13

What is polycythaemia

Answer 13

abnormal increased rbc

hb, rbc and hct/pcv are all increased

Question 14

types of polycythaemia and causes

Answer 14

1. Polycthaemia– reduced plasma volume
   - -dehydrated
2. True polycythaemia - increased RBC volume

Question 15

Causes of increase in total volume of red cells in the circulation leading to true polycythaemia

INAPPROPRIATE– No physiological need

Answer 15

1. Blood doping/ overtransfusion/ erythropoietin administered inappropriately to haematogically normal subjects–
   2.Normal response due to increased EPO, eg hypoxia will cause a physiological increase in EPO APPROPRIATE
2. inappropriate EPO eg EPO from a kidney tumour
3. –independent of eryhropoitin
   Intrinsic problem with the bone marrow leading to inappropriately increased ERYTHROPOIESIS NOT EPO in blood. this is called Polycythaemia vera/ primary polycythaemia. ie a problem independent of EPO stimulus

Question 16

When during the human development is RBC, Hct and Hb the highest?

Answer 16

Neonates (first 28 days after birth) have higher RBC, Hct and Hb than other times of life

Question 17

Men vs Women, Children vs Adults, who has higher RBC Hct and Hb

Answer 17

Men>women

Adults>children (not neonates)

Question 18

define Myeloproliferative Neoplasms

Answer 18

When body produces too much of the myeloid lineage cells, including WBC, RBC and platelets.

Question 19

Name a consequence/complications of polycythaemia

Answer 19

Thick blood/hyperviscosity

=> vascular obstruction

Question 20

Treatment of polycythaemia

Answer 20

1. If there is no physiological need for a high haemoglobin, or if hyperviscosity is extreme, blood can be removed to thin the blood
2. If there is intrinsic bone marrow disease (polycythaemia vera) drugs can be used to reduce bone marrow production of red cells

Question 21

How did Hb used to be measured

Now?

Answer 21

Spectrometer- haemoglobin converted to stable form and measuring light absorption at specific wave length

Same principles, automated instrument

Question 22

++++How did PVC /hct used to be measured

Answer 22

Centrifuging blood sample

Question 23

How was Mean cell volume initally calculated

how is it determined now

Answer 23

Dividing total volume of rbc in a sample by no of rbc

Now determined indirectly by light scattering or interruption of an electrical field

Question 24

Mean cell haemoglobin

Answer 24

Amount of haemoglobin in a given volume of blood divided by the number of red cells in the same volume i.e Hb divided by the RBC

may have same mchc but smaller

Question 25

MCHC– mean cell haemoglobin concentration

Answer 25

Amount of haemoglobin in a given volume of blood divided by the proportion of the sample represented by the rbc– ie Hb divided by Hct

Correlates with hypochromia/hyperchromia

Question 26

Removal of blood

Answer 26

Venesection