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Haematology > Red blood cell paramteres > Flashcards

Red blood cell paramteres Flashcards

1
Q

What is Hct?

A

Haematocrit (l/l), the relative volume of a blood sample that is the red cells (previously known as PCV and expressed as %).

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2
Q

What is WBC?

A

White blood cell count, the number of white cells in a given volume of blood ( x 10^9/l).

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3
Q

What is RBC?

A

Red blood cell count, the number of red cells in a given volume of blood ( x 10^12/l).

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4
Q

What is Hb?

A

Haemoglobin concentration in a given volume of blood (g/l).

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5
Q

What is MCV

A

Mean cell volume, i.e. the average size of the red cells (fL - femtoliter = 1 x 10^-15 L).

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6
Q

What is MCH?

A
  • Mean cell haemoglobin, i.e. the average amount of haemoglobin in a red cell (pg - picogram = 1 x 10^-12 g).
  • The MCH is the absolute amount of haemoglobin in an individual red cell
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7
Q

What is MCHC?

A
  • Mean cell haemoglobin concentration, i.e. the average concentration of haemoglobin in a red cell (g/l).
  • The MCHC is the concentration of haemoglobin in an individual red cell.
  • The MCHC is related to the shape of the cell.
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8
Q

What is platelet count?

A

The number of platelets in a given volume of blood ( x 10^9/l).

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9
Q

Recall the blood parameters equations

A
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10
Q

If we collect everyones data together we have a dataset for red blood cell parameters and can compare males vs females. It is now time to graphically display your data - what assumptions should you check before this?

A

Normality, homogeneity of variance, skewness , kurtosis

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11
Q

Would you consider the following data normally distributed or not?

A

2,6 and 9 are?

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12
Q

Can we delete the erroneous yellow point from our dataset? What if we find out that this patient didn’t take the drug as instructed?

A
  • No
  • Still no if we are considering intent to treat as in the real world people will not take/incorrectly take medication.
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13
Q

Identify as many weaknesses in the figure above as possible.

A

No axis labels, no title, 3D graph without any scale, no units.

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14
Q

How do we assess haematological parameters?

A
  • By obtaining a blood sample
    • Venous sample
    • Finger-prick or heel-prick sample
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15
Q

What parameters from this full blood count are measured and what are calculated?

A
  • Measured - WBC, RBC, Hb, Hct and platelet count
  • Calculated - MCV, MCHC, MCH
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16
Q

How are WBC, RBC and platelet count measured?

A
  • Initially counted visually, using a 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 electrical field
17
Q

How is haemoglobin concentration measured?

A
  • Initially measured in a spectrophotometer, 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.
18
Q

How is haematocrit measured?

A

Initially measured by centrifuging a blood sample so packed cell volume (PCV) was then an appropriate term

19
Q

Why are blood cell parameters important and what needs to be considered when interpreting them?

A
  • The Full Blood Count (FBC) is a frequently performed blood test, often requested routinely both in GP surgeries and in hospitals
  • The 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
20
Q

What happens to the blood sample during polycythaemia?

A
21
Q

What causes polycythaemia?

A
  1. Blood doping or over transfusion
  2. Appropriately increased erythropoietin as a response to hypoxia (at high altitudes with low oxygen or due to cardiac/respiratory disorders).
  3. Inappropriate erythropoietin synthesis or use - result of erythropoietin doping, renal (ep synthesised in kidneys) or other tumours inappropriately increasing ep secretion.
  4. Independent of erythropoietin - Caused by an intrinsic bone marrow disorder called polycythaemia vera (myeloproliferative disorder) among other causes.
22
Q

What problems does polycythaemia cause and how can they be treated?

A
  • Polycythaemia can lead to ‘thick blood’– more technically known as hyperviscosity, which can lead to vascular obstruction and venous or arterial thrombosis
  • Blood can be removed (venesection) to reduce the viscosity
  • Drugs can be given to reduce bone marrow production of red cells
23
Q

List a possible cause and mechanism of a raised haemoglobin concentration (Hb) in:

  1. A patient with an abdominal mass?
  2. A breathless patient with airways disease?
  3. A young healthy athlete?
A
  1. Kidney tumour - inappropriate erythropoietin secretion
  2. Hypoxia - appropriately increased erythropoietin
  3. Blood doping or inapporpriate erythropoietin use
  • Always interpret a blood count in the context of the clinical history and physical findings
24
Q

What is anaemia?

A
  • Reduction in the amount of haemoglobin in a given volume of blood below what would be expected in comparison with a healthy subject of the same age and gender
  • The RBC and the Hct/PCV are usually also reduced
  • Looking at other red blood cell parameters e.g. MCV can help us determine the cause of the anaemia
25
Q

What is the correlation between cell size on a blood film and MCV?

A
26
Q

Which of these has a higher MCV?

A
  • The film on the left has a higher MCV
27
Q

What are some causes of macrocytosis (increased MCV)?

A
  • Vitamin B12 and folate deficiency
  • Haemolysis (polychromasia)
  • Liver disease or ethanol toxicity
  • Pregnancy
  • Young red cells are about 20% larger than mature red cells
  • increased proportion of young red cells (polychromasia/reticulocytes) in circulation will increase average cell size (MCV).
28
Q

What are some causes of microcytosis (decreased MCV)?

A
  • Iron deficiency
  • Defect in α-globin chain synthesis (α thalassaemia)
  • Defect in β-globin chain synthesis (β thalassaemia)
29
Q

How can MCH and MCHC help in distinguishing between iron deficiency microcytosis and thalassemia trait?

A
30
Q

How will the following blood parameters differ from normal in iron deficiency vs thalassemia trait:

  • Haemoglobin (Hb)
  • MCV
  • MCH
  • MCHC
  • RBC
  • Hb electrophoresis
A
31
Q

What can you tell about the red blood cells in this blood film?

A

Normal blood film

32
Q

What can you tell about the red blood cells in this blood film?

A
  • Iron deficiency anaemia
  • Characterised by low MCH and MCHC (hypochromia).
33
Q

What can you tell about the red blood cells in this blood film?

A
  • Thalassaemia trait
  • characterised by low MCH but normal MCHC (hence distorted shape).
34
Q

What would you expect on a normal Hb electrophoresis and on assays of the following conditions:

  • B-thalassaemia trait
  • B-thalassaemia major
  • Sickle cell trait
  • Sickle cell anaemia
A
35
Q

What chains are the following Hb molecules made of:

  • Hb A
  • Hb A2
  • HbS
  • HbF
A
  • Hb A2 contains 2 alpha and 2 delta chains
  • In HbS the B-chain has a single mutation of Glu6 to hydrophobic Val. Under deoxygenated conditions, Val tends to interact with Leu and Phe leading to polymerisation and clumping of HbS).
  • HbF has 2 alpha and 2 gamma chains
  • Hb A has 2 alpha and 2 beta chains
36
Q

What are some reasons to distinguish between iron deficiency anaemia and B-thalassaemia trait?

A
  • To replace iron where this is deficient and not incorrectly prescribe iron supplements that have no effect in thalassaemia trait.
  • To advise individuals with thalassaemia trait on potential risks to future offspring (genetic counselling).
37
Q

What further test may help distinguish between iron deficiency anaemia and B-thalassaemia?

A
  • Iron studies e.g. low serum ferritin (reflects iron stores) probably alludes to iron deficiency anaemia.
38
Q

Which of these has a normal or high MCHC, and which is low?

A
  • One on the left is normal/high, one on right is low.

Haematology (4 decks)

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