Red Cell Parameters Flashcards
Safety considerations
- 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.
What are the basic steps for collecting a capillary blood sample?
- 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.
What is Hct?
Haematocrit (Hct) is the volume of red blood cells as a ratio of whole blood volume.
Equations for MCV, MCH and MCHC
MCV (L) = Hct/RBC
MCH (g) = Hb/RBC
MCHC (g/L) = Hb/Hct
Define MCV, MCH and MCHC
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.
How do we first assess haematological parameters?
Venous sample
Finger-prick or heel=prick sample
What is WBC?
White blood cell count in a given volume of blood (x10^9/L)
What is RBC?
Red blood cell count in a given volume of blood (x10^12/L)
Units for Hb?
g/L
What is Hct?
Previously known as packed cell volume (PCV). Expressed as a %.
Which blood cell parameters are measured?
WBC, RBC, Hb, Hct, platelet count
Which blood cell parameters are derived?
MCV, MCH and MCHC
How do you measure WBC, RBC and platelet count?
(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.
How do you measure Hb?
(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.
How do you measure Hct?
Initially measured by centrifuging a blood sample so PCV was then an appropriate term.
Why are blood cell parameters important?
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.
What does polycythaemia mean?
‘Many cells’ - refers to too many red cell in the circulation.
What values are increased if a patient has polycythaemia?
Hb, RBC and Hct are all increased compared with normal patients of the same age and gender.
What is the difference between pseudo and true polycythaemia?
Pseudo - Reduced plasma volume.
True - Increase in total volume of red cells in the circulation.
What is true polycythaemia often caused by?
Blood doping or over-transfusion.
Appropriately increased EPO
Inappropriate EPO synthesis or use.
Independent of EPO
Explain how excessive blood transfusion and response to hypoxia can lead to true polycythaemia.
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.
What is central cyanosis?
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.
Explain how inappropriate EPO use lead to polycythaemia.
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).
What condition causes polycythaemia that is independent of EPO?
PolyC can result from inappropriately ^ erythropoiesis that is independent of erythropoietin. Condition is an intrinsic bone marrow disorder called POLYCYTHAEMIA VERA
What is polycythaemia vera?
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.
What is another term for polycythaemia?
Erythrocytosis
List a possible cause and mechanism of a raised Hb in a patient with an abdominal mass.
Kidney tumour - inappropriate erythropoietin secretion.
List a possible cause and mechanism of a raised Hb in a breathless patient with airways disease.
Hypoxia - approximately increased erythropoietin.
List a possible cause and mechanism of a raised Hb in a young healthy athlete
Blood doping or inappropriate EPO use.
What is anaemia?
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.
Causes of macrocytosis
Lack of VB12 or folic acid (megaloblastic anaemia)
Liver disease and ethanol toxicity
Haemolysis (polychromasia)
Pregnancy
Causes of microcytosis
Defect in haem synthesis - Iron deficiency
Defect in globin synthesis - Defect in alpha or beta chain synthesis (alpha or beta thalassaemia)
ACD
Difference between MCH and MCHC.
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.
Comparison of Hb, MCV, MCH, MCHC and RBC in IDA vs thalassaemia trait.
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
