Deciding what is normal and interpreting blood count

Question 1

What can the normal range be affected by?

Answer 1

• Age
• Gender
• Ethnic origin
• Physiological status
• Altitude
• Nutritional status
• Cigarette smoking - alcohol intake

Question 2

How is a reference range determined?

Answer 2

• Samples are collected from healthy volunteers with defined characteristics
• They are analysed using the instrument and techniques that will be used for patient samples
• The data are analysed by an appropriate technique

Question 3

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

Answer 3

• A reference range is derived from a carefully defined reference population
• A normal range is a much vaguer concept

Question 4

MCV

Answer 4

• mean cell volume

- fl

Question 5

MCH

Answer 5

• mean cell Hb
• amount of HB in a given cell
• pg

Question 6

MCHC

Answer 6

• Mean cell Hb concentration

- g/l

Question 7

WBC, RBC and platelet count - technique

Answer 7

• initially counted using microscope and diluted sample
• Now 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 8

Hb measurement technique

Answer 8

• Initially measured in a spectrometer, by converting haemoglobin to a stable form and measuring light absorption at a specific wave length
• Now measured by an automated instrument but the principle is the same

Question 9

PCV or Hct measurement

Answer 9

• initially centrifuging and looking at proportion (%)
• measure height of RBC column and give result as percentage
• now: automated instrumented

Question 10

MCV measurement

Answer 10

• Initially calculated be dividing the total volume of red cells in a sample by the number of red cells in a sample, i.e. by dividing the PCV by the RBC
• Now determined indirectly by light scattering or by interruption of an electrical field (seen on histogram)
• cell size as recognised on a blood film

Question 11

MCH

Answer 11

• The amount of haemoglobin in a given volume of blood divided by the number of red cells in the same volume, i.e. the Hb divided by the RBC
• pg

Question 12

MCHC

Answer 12

The amount of Hb in a given volume of blood divided by the proportion of the sample represented by the red cells,
- i.e. the Hb divided by the Hct

Question 13

What is the difference between MCH and MCHC?

Answer 13

• MCH is the absolute amount of haemoglobin in an individual red cell
• In microcytic and macrocytic anaemias, the MCH tends to parallel the MCV
• MCHC is the concentration of haemoglobin in a red cell

Question 14

MCHC measurement

Answer 14

• now measured electronically, most accurately on the basis of light scattering
• These scatter plots compare the MCHC in a severe thalassaemic condition, normal and hereditary spherocytosis

Question 15

How do you interpret a blood count?

Answer 15

• Is there leucocytosis or leucopenia?
• If so, why?
• Which cell line is abnormal?
• Are there any clues in the clinical history?

Is there anaemia?
If so, are there any clues in the blood count?
Are the cells large or small?
Are there any clues in the clinical history?

• Is there thrombocytosis or thrombocytopenia?
  If so, are there any clues in the blood count?
  Are there any clues in the clinical history?

Question 16

What results should you look at first?

Answer 16

• WBC and differential (don’t only look at percentage, also look at the absolute count)
• Hb
• MCV
• Platelet count

Question 17

Why is there a high platelet count in SCA?

Answer 17

• splenic inadequacy

- platelet count tends to rise if the spleen is hypofunctional

Question 18

Polycythaemia

Answer 18

• too many RBCs in the circulation

- Hb, RBC and Hct/PCV are all increased compared with normal subjects of the same age and gender

Question 19

Pseudo-polycythaemia

Answer 19

• not that common

- due to reduced plasma volume

Question 20

True polycythamia causes

Answer 20

• Blood doping or overtransfusion
• Appropriately increased erythropoietin (e.g. hypoxia, high altitude)
• Inappropriate erythropoietin synthesis or use (e.g. cyclists)
• independent use of erythropoietin
• medical negligence (e.g. too much blood transfused)
• renal or other tumor secreting erythropoietin
• abnormal function of bone marrow (e.g. polycythaemia vera)

Question 21

How do you evaluate polycythaemia?

Answer 21

• clinical history and physical examination (splenomegaly, abdominal mass or cyanosis could be relevant)
• compare with an appropriate normal range
• ask if it I genuine or only apparent

Question 22

Polycythamia vera

Answer 22

• neoplastic condition of the bone marrow
• myeloproliferative neoplasm
• too much production of RBCs

Question 23

Why is polycythemia from a kidney tumour quite common?

Answer 23

Because it is the normal site of erythropoietin production

Question 24

Abnormal function of bone marrow as a cause for polycythaemia

Answer 24

• Inappropriately increased erythropoiesis that is independent, or largely independent, of erythropoietin
• This condition is an intrinsic bone marrow disorder called polycythaemia vera
• classified as a myeloproliferative neoplasm

Question 25

How do you take care of polycythaemia/

Answer 25

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

Question 26

What is the appropriate statistical technique for deterimining a (reference) range?

Answer 26

• Data with a normal (Gaussian) distribution can be analysed by determining the mean and standard deviation and taking mean ± 2SD as the 95% range
• Data with a different distribution must be analysed by an alternative method

Question 27

WBC
RBC
Hb
Act
PCV

-> Einheiten

Answer 27

WBC – white blood cell count in a given volume of blood (× 109/l)
RBC – red blood cell count in a given volume of blood (× 1012/l)
Hb – haemoglobin concentration (g/l)
Hct – haematocrit (l/l)
PCV – packed cell volume (% or l/l) (an older name for the Hct)

Question 28

How does a cell look under the microscope if the MCHC is reduced?

Answer 28

larger area of central pallor

Question 29

What would you suspect in a patient with leukocytosis and thrombocytosis?

Answer 29

Maybe Leukaemia

-> do a differential WBC

Question 30

How are certain blood values different in age and gender?

Answer 30

• Hb, RBC and Hct are higher in the neonate than at other times of life, lower in children than in adults
• lower in women than in men

Question 31

Apparent vs. genuine polycythaemia

Answer 31

• high Hb, RBC and PCV/Hct can result from a decrease in plasma volume, referred to as ‘pseudopolycythaemia’ or ‘apparent polycythaemia’
• When the abnormalities result from an increase in the number of circulating red cells there is a true polycythaemia

Question 32

residents of the Tibetan plateau have a 85% prevalence of a mutation that reduces the erythropoietin production in response to hypoxia - WHY?

Answer 32

• To reduce the viscosity of blood

- high altitude would generally be associated with hypoxia and increased erythropoietin

Question 33

What is the danger of polycythaemia vera?

Answer 33

• Polycythaemia can lead to ‘thick blood’– more technically known as hyperviscosity
• This can lead to vascular obstruction

Question 34

How do you interpret a blood count?

Answer 34

Always interpret a blood count in the context of the clinical history and physical findings

-> Is this normal for THIS patient?