Deciding what is normal and interpreting a blood count

Question 1

Full blood count components

Answer 1

• WBC (white blood cell count in a given volume of blood x 10^9/l)
• RBC (red blood cell count in a given volume of blood x 10^12/l)
• Hb (haemoglobin concentration g/l)
• PCV (packed cell volume)
• Hct (haematocrit)
• MCV (mean cell volume fl)
• MCH (mean cell haemoglobin pg)
• MCHC (mean cell haemoglobin concentration g/l)
• platelet count (the number of platelets in a given volume of blood x 10^9/l)

Question 2

PCV (or Hct) measurement

Answer 2

Initially measured by centrifuging blood sample

Question 3

MCH

Answer 3

Amount of haemoglobin in a given volume of blood/number of RBCs in the same volume
MCH=Hb/RBC
-follows MCV in microcytic and macrocytic anaemia

Question 4

MCHC

Answer 4

Amount of haemoglobin in a given volume of blood/ the proportion of the sample formed of RBCs
MCHC=Hb/Hct
-related to the cell shape

Question 5

MCH vs MCHC

Answer 5

MCH=absolute amount of haemoglobin in an individual RBC

MCHC=haemoglobin concentration in a RBC

Question 6

MCV

Answer 6

Initial calculation: total volume of RBCs in a sample/ number of RBCs in a sample
MCV=(PCV x 1000)/RBC
-Now determined indirectly by light scattering or by interruption of an electrical field

-cell size on a blood film correlates with MCV

Question 7

Reference range

Answer 7

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Question 8

Normal range

Answer 8

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Question 9

Factors affecting what is considered normal

Answer 9

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

Question 10

Normally distributed (Gaussian distribution) data analysis

Answer 10

-determine mean and standard deviation (95% range calculated as mean +/- 2 standard deviation)

Question 11

Non-Gaussian distribution data analysis

Answer 11

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Question 12

Caveats

Answer 12

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Question 13

Hb measurement

Answer 13

• initially used spectrometer (converts haemoglobin to stable form and measuring light absorption at a specific wavelength)
• principle remains but automated instrument used now

Question 14

WBC, RBC and platelet counts

Answer 14

• initially counted visually (microscope use and diluted blood sample)
• now counted in large automated instruments->enumerating (counting) electronic impulses generated when cells flow between light source and sensor, or when cells flow through an electrical field

Question 15

Causes of polycythaemia (too much blood)

Answer 15

-from blood doping or overtransfusion

Question 16

Causes of polycythaemia (appropriately raised erythropoietin levels)

Answer 16

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Question 17

Causes of polycythaemia (abormal function of bone marrow)

Answer 17

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Question 18

Causes of polycythaemia (too much erythropoietin)

Answer 18

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Question 19

Polycythaemia vera

Answer 19

• intrinsic bone marrow disorder whereby bone marrow makes too many RBCs (raised RBC count)-> results in hyperviscosity which can lead to vascular obstruction
• rare type of blood cancer
• classified as a myeloproliferative neoplasm

Question 20

Blood count interpretation

Answer 20

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