Red Cell Parameters

Question 1

Safety considerations

Answer 1

• Do not share/reuse lancets/needles, and dispose of them in the special “sharps” bin provided.
• Clean skin with an alcohol swab before puncture.
• Protect the wound site with a plaster.
• Wear a disposable apron, and put on protective gloves to handle any blood.
• Wash your hands immediately if they accidentally come into contact with blood.
• Spills of blood must be decontaminated immediately (ask a demonstrator).
• At the end of the experiment dispose of glassware and anything which has come into contact with blood in the sharps bin.

Question 2

What are the basic steps for collecting a capillary blood sample?

Answer 2

• Step 1: Explain the test to the donor and gain consent
• Step 2: Have them clean their hands - put gloves on yours. Ask the donor to alcohol gel their hands. Give the alcohol time to evaporate. You should put on a pair of suitably sized nitrile gloves. Use an alcohol swap to wipe clean a suitable puncture site. Allow this to evaporate.
• Step 3: Puncture using a lancet - Use a disposable lancet to puncture the skin at your chose site by pressing firmly and pushing the button on the top. Use a cotton swab to clean the first drop of blood away.
• Step 4: Tender loving care - Give donor a piece of cotton wool to hold on the puncture site. Once the site has stopped bleeding you should apply a plaster.

Question 3

What is Hct?

Answer 3

Haematocrit (Hct) is the volume of red blood cells as a ratio of whole blood volume.

Question 4

Equations for MCV, MCH and MCHC

Answer 4

MCV (L) = Hct/RBC

MCH (g) = Hb/RBC

MCHC (g/L) = Hb/Hct

Question 5

Define MCV, MCH and MCHC

Answer 5

MCV - Average volume of each red cell.

MCH - Average mass of Hb in each red cell.

MCHC - Average concentration of Hb in each red cell.

Question 6

How do we first assess haematological parameters?

Answer 6

Venous sample

Finger-prick or heel=prick sample

Question 7

What is WBC?

Answer 7

White blood cell count in a given volume of blood (x10^9/L)

Question 8

What is RBC?

Answer 8

Red blood cell count in a given volume of blood (x10^12/L)

Question 9

Units for Hb?

Answer 9

g/L

Question 10

What is Hct?

Answer 10

Previously known as packed cell volume (PCV). Expressed as a %.

Question 11

Which blood cell parameters are measured?

Answer 11

WBC, RBC, Hb, Hct, platelet count

Question 12

Which blood cell parameters are derived?

Answer 12

MCV, MCH and MCHC

Question 13

How do you measure WBC, RBC and platelet count?

Answer 13

(Initially counted visually using microscope and a diluted sample of blood.)

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 electric field.

Question 14

How do you measure Hb?

Answer 14

(Initially measured in a spectrometer, by converting Hb to a stable form and measuring light absorption at a specific wavelength.)

Now measured by an automated instrument, but principle is same.

Question 15

How do you measure Hct?

Answer 15

Initially measured by centrifuging a blood sample so PCV was then an appropriate term.

Question 16

Why are blood cell parameters important?

Answer 16

FBC frequently performed → requested routinely.
Vast majority of patients will have a FBC checked during a hospital admission. Doing on a daily basis.
Correct interpretation of a blood count may also require examination of a blood film; films are prepared following the finding of an abnormality in one of (or more than one) of the blood cell parameters.
Always interpret a blood count in the context of the clinical history and findings on physical examination.

Question 17

What does polycythaemia mean?

Answer 17

‘Many cells’ - refers to too many red cell in the circulation.

Question 18

What values are increased if a patient has polycythaemia?

Answer 18

Hb, RBC and Hct are all increased compared with normal patients of the same age and gender.

Question 19

What is the difference between pseudo and true polycythaemia?

Answer 19

Pseudo - Reduced plasma volume.

True - Increase in total volume of red cells in the circulation.

Question 20

What is true polycythaemia often caused by?

Answer 20

Blood doping or over-transfusion.
Appropriately increased EPO
Inappropriate EPO synthesis or use.
Independent of EPO

Question 21

Explain how excessive blood transfusion and response to hypoxia can lead to true polycythaemia.

Answer 21

Polycythaemia can result from the action of EPO that is appropriately elevated e.g. as a result of hypoxia. In some situations such as altitude this may be beneficial.

Question 22

What is central cyanosis?

Answer 22

Blue discolouration seen on the tongue and lips due to lower levels of oxygen in arterial circulation (hypoxia) caused by some cardiac or respiratory disorders.

Question 23

Explain how inappropriate EPO use lead to polycythaemia.

Answer 23

EPO inappropriately administered e.g. cyclists.

OR

When a kidney (renal) or other tumour inappropriately secretes erythropoietin. (Not surprising since the kidneys normally produce erythropoietin).

Question 24

What condition causes polycythaemia that is independent of EPO?

Answer 24

PolyC can result from inappropriately ^ erythropoiesis that is independent of erythropoietin. Condition is an intrinsic bone marrow disorder called POLYCYTHAEMIA VERA

Question 25

What is polycythaemia vera?

Answer 25

Classified as a myeloproliferative disorder. Can lead to thick blood - hyperviscosity → Leads to vascular obstruction and venous or arterial thrombosis.

Blood can be removed (venesection) to reduce viscosity.

Drugs can be given to reduce bone marrow production of red cells.

Question 26

What is another term for polycythaemia?

Answer 26

Erythrocytosis

Question 27

List a possible cause and mechanism of a raised Hb in a patient with an abdominal mass.

Answer 27

Kidney tumour - inappropriate erythropoietin secretion.

Question 28

List a possible cause and mechanism of a raised Hb in a breathless patient with airways disease.

Answer 28

Hypoxia - approximately increased erythropoietin.

Question 29

List a possible cause and mechanism of a raised Hb in a young healthy athlete

Answer 29

Blood doping or inappropriate EPO use.

Question 30

What is anaemia?

Answer 30

Reduction of Hb in a given volume of blood below what would expected in comparison with a healthy subjects of same age and gender.

By definition → Hb is reduced.

RBC and Hct/PCV are usually also reduced.

Question 31

Causes of macrocytosis

Answer 31

Lack of VB12 or folic acid (megaloblastic anaemia)
Liver disease and ethanol toxicity
Haemolysis (polychromasia)
Pregnancy

Question 32

Causes of microcytosis

Answer 32

Defect in haem synthesis - Iron deficiency

Defect in globin synthesis - Defect in alpha or beta chain synthesis (alpha or beta thalassaemia)

ACD

Question 33

Difference between MCH and MCHC.

Answer 33

MCH is absolute amount of Hb in an individual red cell.
MCHC is concentration of Hb in a red cell.
MCH measures average amount of Hb in an individual red cell.
MCHC is related to the shape of the cell.

Question 34

Comparison of Hb, MCV, MCH, MCHC and RBC in IDA vs thalassaemia trait.

Answer 34

Hb:
IDA - Normal or low
TT - Normal (or mildly low)

MCV:
IDA - Low in proportion to Hb
TT - Lower for same Hb

MCH:
IDA - Low in proportion to Hb
TT - Lower for same Hb

MCHC:
IDA - Low
TT - Relatively preserved

RBC
IDA - Low
TT - Increased