Haematology. pulses and blood pressure Flashcards
What is haematology?
The study of normal and pathologic aspects of blood and blood cells
What is an erythrocyte?
Also known as a red blood cell. These biconcave discs lack a nucleus but contain haemoglobin (Hb) which allows oxygen to be transported to respiring tissues
What is a leukocyte?
generic name for white blood cell. Mainly function as part of the bodies defence. Examples are granulocytes: neutrophils, basophils and eosinophils and agranulocytes: monocytes and lymphocytes
What are the formed elements?
The cellular and cell fragment components of blood: cells (erythrocytes and leukocytes), platelets (thrombocytes) which are suspended in the plasma
What is plasma?
The straw coloured liquid component of blood made up of water, electrolytes and proteins
What is an antibody and antigen?
A protein produced by the immune system. Also called immunoglobulins. Produced in response to a foreign substance (antigen). Antibodies recognise specific antigens and bind to them so they can be removed from the body
What is blood pressure?
Pressure of force that moves circulating blood around the body through our circulatory system, specifically measured in our arteries. Blood pressure readings consist of two number: the systolic pressure first and the diastolic pressure second. Readings are given in mmHg
What is the systolic phase?
The phase of cardiac cycle when the ventricles are contracting. This is the higher of the two numbers
What is the diastolic phase?
The phase of the cardiac cycle when the ventricles are relaxing. This is the lower of the two numbers
What are things to note about health and safety to do with this practical?
- PPE should be worn whenever we are handling human tissue or human body fluid (blood)
- Gloves should be worn at all times – blood should never be handled directly
- Individuals who appear healthy may be carriers of infectious hepatitis
- Risk of HIV transmission
- Treat all blood as infected
- Dispose all used or contaminated items the correct way in the correct place
What does blood do?
- Transports gases
- Carries nutrients, hormones, waste products and heat
- Involved in inflammation and contains antibodies which are responsible for the recognition and destruction of foreign micro-organisms and for triggering the immune response.
What does blood consist of?
Plasma and formed elements
What does plasma play roles in?
immunity, transport and osmotic effects
What are the formed elements of the blood involved in?
gas transport, immunity and the arrest of bleeding (haemostasis)
What type of blood sample could be collected for a blood test?
venous or capillary
What is the procedure for obtaining a sample of capillary blood using a single lancet?
- Wipe finger with alcohol wipe and allow to dry (otherwise blood will smudge and it will be hard to obtain the sample)
- Massage bottom of finger gently
- Press the lancet against your finger and then push on the button
- It will always retrieve safely after use
- Dispose of the lancet in the yellow bin
- Squeeze the bottom of the finger until blood comes out
give examples of uses of small finger prick samples
- Blood glucose levels
- Cholesterol testing
- Haemoglobin levels
- Covid antibody tests (trial June 2020)
- Used in laboratory tests e.g. making a blood smear to view blood cells
Is it easier to obtain good sample from a finger tip if the hand is warm of cold?
warm
What is venepuncture and when is it used?
- Where blood is taken directly from a vein in the forearm
- it is used when larger samples of blood are needed
How is venepuncture carried out?
- A tourniquet is placed around the upper arm to allow blood to pool in the vein making the vein easier to identify and enables the sample to be taken when a small needle is inserted directly into the vein
- A sample obtained by venepuncture is collected directly into a bottle containing an anti-coagulant such as EDTA (ethylene-diaminetetraacetic acid), a chelating agent that binds to calcium
What is a haemocytometer?
A specially ruled chamber
What is the manual method for measurement of blood cells?
pipetting a diluted blood sample into haemocytometer (a specially ruled chamber) and then observing it under a microscope
What are red blood cell counts and what are they used to do?
- they are commonly performed haematology tests that are usually part of the full or complete blood count
- the RBC count approximates the number of circulating red blood cells and is helpful in diagnosing and treating many diseases, especially anaemias
What other cells counts is a haemocytometer used for?
cell counts in semen and cerebrospinal fluid samples
What does a haemocytometer consist of?
• A haemocytometer consists of surface-patterned two enclosed chambers with two ports for sample injection
/how is the 10 ul sample of capillary blood diluted for our red blood cell count?
- The diluting fluid for the red blood cell count is 0.9% saline and a preservative. This is an isotonic saline solution which is necessary to prevent haemolysis or destruction of the red blood cells
- 1.99ml of saline is added to the 10ul blood. This will provide a 200 fold dilution (dilution by the factor 200)
- 10ul of the cell/suspension is then taken up using a pipette for adding to the haemocytometer
Why can you use one haemocytometer to count independent samples?
Because there are two entirely separate chambers
What are the counting areas of the haemocytometer?
- The haemocytometer contains two identical ruled areas composed of etched lines that define squares of specific dimensions. These are in the detection areas A and B
- The detection areas A and B are separate enclosed areas. In each is a chamber which confines the fluid (blood and saline mixture) when the chamber is filled and regulates the depth of the fluid.
- In the detection area there are ruled areas consisting of a large square, 3mmx3mm, divided into nine equal squares, each 1mm square (1mm^2). The total of the large square is 9mm^2
- There are different areas designated for counting white blood cells and red blood cells
- The WBC counting area consists of large squares denoted with ‘W’ and for RBC denoted with ‘R’
- We only use the large centre square for the RBC count. This square is subdivided into 25 smaller squares which in turn are divided into 16 squares. Of the 25 squares only the four corner squares and the centre square are used to perform RBC counts
How do you count the cells in a haemocytometer?
• Each of the 5 squares we use to count the red blood cells in turn contains 4 rows of squares. All cells within each of the small squares are counted using the left to right, right to left counting pattern
• When counting RBC using the haemocytometer there are some rules to follow:
- The cells touching either the top or left boundaries of the squares are included in the count
- The cells touching the right boundary and the cells touching the lower boundary of each square are not counted
- Cells lying beyond these boundaries are not counted in the red blood cell count.
- If the number of cells in a square varies from any other square on the same side of the haemocytometer by more than 25 cells the count must be repeated (remixed and reloaded to the haemocytometer) ensuring the most accurate and precise results
How do you calculate the number of red blood cells per ml?
- (total cells in 5 squares/5) x 25 x 200(dilution factor) x 10^4 (volume factor)
- Each square has a total volume of 0.1mm^3 (0.1ul) therefore a volume factor of 10 000 (10^4) is needed to obtain the number of red blood cells per ml
- The reading for the red cell count should be multiplied by 10^12 (maybe 10^7 but check) to give the number of red cells per litre. This is the usual format in which these results are expressed
What is the normal RBC count values for women?
3.9-5.6 x 10^12 per litre (10^9 per ml or 10^6 per ul) (female)
What is the normal RBC count for men?
4.5-6.5 x 10^12 per litre (19^9 per ml or 10^6 per ul)
What does haemoglobin (Hb) allow?
the carriage of oxygen from the lungs to the tissues
What is the structure of a Hb molecule (simply)?
Each haemoglobin molecule exists as a tetramer, made up of 4 peptide chains (globins) with its associated haem molecule
What are the methods that Hb concentration can be estimated based on?
the intensity of colour (or light absorption) of a stable derivative of haemoglobin.
In our method what is haemoglobin converted to?
the stable coloured derivative azidemethaemoglobin
What is the normal range for haemoglobin concentrations for women?
120-160 g L^-1 (12-16 g/dL)
What is the normal range for haemoglobin concentrations for men?
135-175 g L^-1 (13.5-17.5 g/dL)
What is the haematocrit/ packed cell volume (PCV)
- This refers to the volume of red blood cells expressed as a proportion of the total volume of a blood sample.
- The remaining volume of the sample consists of the buffy coat (leucocytes and platelets which are usually negligible) and plasma.
- The proportion of RBCs (also described as the ‘haematocrit) may be expressed either as a decimal or percentage
How can haemoglobin and haematocrit measurements be obtained?
using a point of care (hand held) device. This is known as ‘point of care testing’ which, in contrast to counting red blood cells using a haemocytometer is an automated method which provides results in approximately 12 seconds