Red blood cell paramteres Flashcards
What is Hct?
Haematocrit (l/l), the relative volume of a blood sample that is the red cells (previously known as PCV and expressed as %).
What is WBC?
White blood cell count, the number of white cells in a given volume of blood ( x 10^9/l).
What is RBC?
Red blood cell count, the number of red cells in a given volume of blood ( x 10^12/l).
What is Hb?
Haemoglobin concentration in a given volume of blood (g/l).
What is MCV
Mean cell volume, i.e. the average size of the red cells (fL - femtoliter = 1 x 10^-15 L).
What is MCH?
- 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
What is MCHC?
- 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.
What is platelet count?
The number of platelets in a given volume of blood ( x 10^9/l).
Recall the blood parameters equations
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?
Normality, homogeneity of variance, skewness , kurtosis
Would you consider the following data normally distributed or not?
2,6 and 9 are?
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?
- No
- Still no if we are considering intent to treat as in the real world people will not take/incorrectly take medication.
Identify as many weaknesses in the figure above as possible.
No axis labels, no title, 3D graph without any scale, no units.
How do we assess haematological parameters?
- By obtaining a blood sample
- Venous sample
- Finger-prick or heel-prick sample
What parameters from this full blood count are measured and what are calculated?
- Measured - WBC, RBC, Hb, Hct and platelet count
- Calculated - MCV, MCHC, MCH
How are WBC, RBC and platelet count measured?
- 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
How is haemoglobin concentration measured?
- 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.
How is haematocrit measured?
Initially measured by centrifuging a blood sample so packed cell volume (PCV) was then an appropriate term
Why are blood cell parameters important and what needs to be considered when interpreting them?
- 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
What happens to the blood sample during polycythaemia?
What causes polycythaemia?
- Blood doping or over transfusion
- Appropriately increased erythropoietin as a response to hypoxia (at high altitudes with low oxygen or due to cardiac/respiratory disorders).
- Inappropriate erythropoietin synthesis or use - result of erythropoietin doping, renal (ep synthesised in kidneys) or other tumours inappropriately increasing ep secretion.
- Independent of erythropoietin - Caused by an intrinsic bone marrow disorder called polycythaemia vera (myeloproliferative disorder) among other causes.
What problems does polycythaemia cause and how can they be treated?
- 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
List a possible cause and mechanism of a raised haemoglobin concentration (Hb) in:
- A patient with an abdominal mass?
- A breathless patient with airways disease?
- A young healthy athlete?
- Kidney tumour - inappropriate erythropoietin secretion
- Hypoxia - appropriately increased erythropoietin
- Blood doping or inapporpriate erythropoietin use
- Always interpret a blood count in the context of the clinical history and physical findings
What is anaemia?
- 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
What is the correlation between cell size on a blood film and MCV?
Which of these has a higher MCV?
- The film on the left has a higher MCV
What are some causes of macrocytosis (increased MCV)?
- 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).
What are some causes of microcytosis (decreased MCV)?
- Iron deficiency
- Defect in α-globin chain synthesis (α thalassaemia)
- Defect in β-globin chain synthesis (β thalassaemia)
How can MCH and MCHC help in distinguishing between iron deficiency microcytosis and thalassemia trait?
How will the following blood parameters differ from normal in iron deficiency vs thalassemia trait:
- Haemoglobin (Hb)
- MCV
- MCH
- MCHC
- RBC
- Hb electrophoresis
What can you tell about the red blood cells in this blood film?
Normal blood film
What can you tell about the red blood cells in this blood film?
- Iron deficiency anaemia
- Characterised by low MCH and MCHC (hypochromia).
What can you tell about the red blood cells in this blood film?
- Thalassaemia trait
- characterised by low MCH but normal MCHC (hence distorted shape).
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
What chains are the following Hb molecules made of:
- Hb A
- Hb A2
- HbS
- HbF
- 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
What are some reasons to distinguish between iron deficiency anaemia and B-thalassaemia trait?
- 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).
What further test may help distinguish between iron deficiency anaemia and B-thalassaemia?
- Iron studies e.g. low serum ferritin (reflects iron stores) probably alludes to iron deficiency anaemia.
Which of these has a normal or high MCHC, and which is low?
- One on the left is normal/high, one on right is low.
