Blood Components Flashcards
What are red cells?
A standard red cell component in additive solution contains:
– Red cells (Hct 0.50-0.70 and Hb content > 40g/unit)
– 5-30ml of plasma,
– 100 ml of SAG-M solution
Standard red cell units contain no functional platelets, granulocytes or coagulation factors
Red cells in additive solution can also be collected by apheresis
Stored at 4°C for max. 35 days
When and why are red cells used?
Red cells are transfused to raise the oxygen-carrying capacity of the blood when it is symptomatically reduced due to red cell loss or reduced erythropoiesis
Aims to achieve a fast increase in the supply of oxygen to the tissues, thereby preventing tissue hypoxia
Considered when the concentration of haemoglobin (Hb) is low
– Haemorrhage – trauma, surgery
– Anaemia
– haemoglobinopathy
BUT should only be based on assessment of the patients’ clinical status:
- Is the patient symptomatic? (Hb levels low?)
– Is the anaemia chronic or acute?
– Is the patient likely to resume physical activities immediately?
– Is there history of heart/respiratory disease?
– Is the patient septic/in heart failure?
– Is the anaemia correctable by measures other than transfusion?
Typically only used in: – Acute Blood Loss – trauma, surgery – Hb <70g/L – Post chemotherapy – Post radiotherapy – Chronic Anaemia
In general, one unit of packed red cells raises the Hb concentration in an average sized adult by approximately 10 gL and Hct by 3%
When should frozen red cells be used?
Use frozen red cells for patients with unusual phenotypes when liquid-preserved blood cannot be sourced
- E.g. Bombay Phenotype
Also used for autologous collections – scheduled surgery
These are for patients with rare red cell phenotypes or multiple red cell antibodies present that could destroy donor cells
When are phenotyped components used?
Patients receiving repeated transfusions are exposed to many antigens from the different donors – not ABO or RhD incompatible
Over time, recipient produces antibodies to these
Upon next exposure to the antigen from another transfusion, this can cause a reaction
Phenotyped products – we know what antigens the donor is expressing – prevents ALLOIMMUNISATION – Select ANTIGEN-NEGATIVE BLOOD
When is CMV seronegative blood used?
This Herpes virus is common throughout our population
Competent immune system keeps it under control – individual is free from symptoms
If CMV+ blood is given to foetus/neonate/pregnant women, immature immune system is overwhelmed – serious disease
These patients are given CMV seronegative blood
CMV is associated with cellular blood products (RBCs, Platelets)
When are irradiated blood products used?
Lymphocytes are removed from ALL blood products via LEUKODEPLETION
99.99% successful – presence of residual lymphocytes
In some immunocompromised patients, residual lymphocytes have capacity to mount an immune response against the host – GRAFT VERSUS HOST DISEASE
IRRADIATION of the component destroys nucleated cells
- Red cells remain unaffected
- Use of irradiated components has been proven to reduce the
incidence of TA-GvHD
- Indicated in a number of clinical conditions, e.g. Pre-natal, neonatal, stem cell transplant patients
When are washed red cells used?
Production of red cell components from centrifugation of whole blood leaves some residual donor plasma
This contains high levels of plasma proteins
Not a problem in most transfusion cases
Some recipients may react with plasma proteins –allergy reaction
Washed red cells - removes unwanted plasma proteins, including antibodies.
Patients with reactions to transfused plasma proteins (eg, IgA deficiency)
Patients with severe allergic reactions of unknown cause
How are platelets separated?
Random donor platelets - derived from pooling platelets together from four ABO identical whole blood donations - resuspended in plasma from one of the four donors (50% of donations)
…OR
Single donor platelets - obtained from one donor by the process of apheresis (50% of donations)
Apheresis and pooled platelets are functionally equivalent and can be used interchangeably
However, recipients <16yrs age are transfused with apheresis-obtained platelets in order to minimise their exposure to multiple donors
– reduces the risk of transfusion-transmitted infections
What is the importance of ABO compatibility for platelets?
Despite expressing ABO antigens, it is not essential that patients
receive ABO-matched platelet units
ABO matched platelets are the ideal product
ABO mis-matched products are often used – not really a problem in terms of the platelets themselves, but can be a problem if the plasma they are in contains high-titre ABO antibodies (e.g. If the platelets come from a group O donor with very high levels of anti-A/anti-B)
Group O platelets should only be used for group A, B and AB patients if they are negative for high titre anti-A and anti-B
When are washed platelets used?
Treatment or prevention of life-threatening bleeding
Three basic questions when considering platelet transfusion:
- Does patient have enough platelets (thrombocytopenia)
- Are the platelets working (thrombocytopathy)
- Is the patient bleeding? – most important question
Should really only transfuse if patient is bleeding but large number of units are given prophylactically – necessary?
What is fresh frozen plasma?
FFP collected from whole blood - 200-250mls in one unit
700-800ml can be collected by apheresis – FFP is not usually the target component – collected in addition to platelets
Plasma is separated and stored at ≤ -25°C – this can be kept for 36 months
FFP is a rich source of: – Coagulation factors – Anticoagulation Factors – Fibrinogen (approx. 400mg in each FFP unit) – IgG – Albumin
When is FFP used?
Therapeutic indications – these are well defined
Use it for patients with a coagulopathy, who are bleeding or at risk of bleeding, and where a specific therapy or factor concentrate is not appropriate or unavailable
– Bleeding
– Multiple coagulation deficiencies
– Others
Prophylactic use – patients at risk of bleeding given FFP to ‘correct’ their coagulopathy – this is not common nowadays
Multiple Coagulation Factor deficiency maybe caused by:
– A dilution effect – e.g. after massive transfusion
– Coagulation factor consumption – e.g. DIC
– Decreased production – hepatic failure
In all these cases FFP is used to replace all the coagulation factors - makes the recipient haemostatic
TTP
Trauma patients in a 1:1 ratio with red cells
FFP should be ABO-compatible with recipient red cells
- Don’t have to match for RhD
- Group AB plasma may be given in emergency situations – contains
no A or B antibodies – group AB is rare though
How is FFP used to treat TTP?
Also, commonly used to treat Thrombotic thrombocytopenic purpura (TTP):
- characterised by the formation of micro-thrombi within the circulation
- Typically caused by an enzyme deficiency – ADAMTS13 or
autoantibodies to ADAMTS13
- Normally, ADAMTS13 cleaves vWF into functional units
- Enzyme is deficient/non-functional - patient has large vWF multimers
which are anchored to endothelial cell
- Passing platelets adhere to vWF multimers and form platelet
aggregates – microthrombi (typically in the brain and kidneys)
- Standard of care for TTP is using plasma exchange using apheresis
machine
- Removing the patient’s plasma containing ADAMTS13 autoantibodies
- Replacing with fresh plasma containing normal amounts of
ADAMTS13 and no auto-antibodies
What is cryoprecipitate?
Concentrated blood component made from FFP
The FFP is slowly thawed to 1-6ºC
The resulting ‘murky’ precipitate is then separated from the supernatant and re-frozen for storage at -25ºC for a maximum of 36 months
One unit contains approx. 20-40ml
Contains high levels of fibrinogen, vWF, FVIII, FXIII and fibronectin
When is cryoprecipitate used?
Used in situations where a patient has low levels of fibrinogen, or where the fibrinogen is not working as it should do
Used in surgical/trauma situations where fibrinogen <0.8g/L
Patients with severe liver disease have low fibrinogen
Contains high levels of factor VIII and Factor XIII BUT is rarely used to treat patients with deficiencies in these due to better success with other blood components
Like FFP, cryoprecipitate should be ABO compatible with the patient
Transfusion of this component exposes the recipient to multiple donors as it is usually transfused in pools of up to 6 donor units
It is therefore reserved for patients whose fibrinogen levels remain critically low <1g/L
This product was once just a waste product but evidence suggests that due to its lower levels of vWF, it may be useful in patients with TTP
