TS2 Flashcards
Why do we transfuse blood?
- Red cells – for O2 carrying capacity
- Platelets – for haemostasis.
- Neutrophils – to fight infection. Antibiotics are getting less effective, so an emergency transfusion from neutrophils, although rare, can be used.
- Plasma – to replace coagulation factors/ osmotic properties.
- Plasma-derived products
- Individual coagulation factors. Most are made from recombinant technologies nowadays.
- Albumin
- Immunoglobulin
- Whole blood rarely given – divided into specific components.
Where are red cells used?
Acute blood loss
Anaemia in critical care
Chronic anaemia
Peri-operative transfusion
Where are platelets used?
Bone marrow failure Platelet function disorders DIC Autoimmune thrombocytopenia NAIT (Neonatal alloimmune thrombocytopenia) Massive transfusion
Where is plasma used?
Factor deficiencies
DIC
TTP (Thrombotic thrombocytopenic purpura)
Surgical bleeding
Who can donate blood?
Normal healthy donors aged 17-70 (60 if first time)
Who is excluded from donating blood?
Those who are anaemic
Those at high risk of transmitting infection:
- IV drug users
- Recent tattoos or body piercings
- Recent visitors to the tropics
- Had recent operation, immunisation or vaccination
- Had sex with anyone in high risk group
- Had blood transfusion
How many people give blood?
6% of the population
In 2004 a new rule was introduced that people who had received a transfusion themselves can’t give blood.
Why was this?
They were afraid that variant CJD could be transmitted and was proven to be the case. It is a prion protein, so there is no test for it. There is also a long incubation for it.
Describe the blood preparation process
Blood Donation Packs are split into a testing pack, which goes to the lab for testing and a collection bags containing CPD (an anticoagulant – Citrate Phosphate Dextrose)
It is then passed through a filter to let the blood separate and remove the white blood cells (leukodeplete). Leukodepletion was introduced to reduce variant CJD incidence.
The leukodepleted bags are then centrifuged to separate the blood into its component parts.
Blood bags are then labelled fully, including the patient receiving the blood.
Describe the process of Leukodepletion
Blood is passed through a four-stage filter (Gel, aggregate remover, 2 layers of polyester or polyurethane fibres)
Gel removes small aggregates and clots
Polyester or polyurethane fibres remove leukocytes
This process reduces the leukocyte count to 5x10^6 per unit in 99% of components (95% confidence limits)
Which countries routinely leukodeplete blood?
UK
Ireland
France
Portugal
Why does the USA not routinely filter blood?
Leukodepletion is not done in the USA, as they didn’t have mad cow disease, or at least there was no system in place to ensure the cases of BSE were reported.
What are the advantages of Leukodepletion?
Reduces risk of viral and prion infection
Reduces risk of immunological complications
What are the disadvantages of Leukodepletion?
Cost
Hypotensive episodes from bedside filters
“Red Eye” Syndrome
What are the 3 methods for viral inactivation of blood products?
Solvent detergent (works for plasma) Metheylene blue (works for plasma) Psoralens (S-59) (works for platelets)
Describe the features of the solvent detergent method for viral inactivation of blood products
Disrupts lipid envelope of HIV and hep B, hep C viruses
Ineffective against non-lipid coated viruses (hep A,
parvovirus B19)
Describe the features of the methylene blue method for viral inactivation of blood products
Generates ROS when exposed to white light, damages
DNA and RNA and prevents viral replication
Describe the features of the psoralens (s-59) method for viral inactivation of blood products
Binds to DNA and RNA - rendered irreversible by UVA
What are blood donations screened for?
Obligatory testing
- hep B, hep C, HIV-1, 2, syphilis, HTLV-I, II
Sometimes tested
- CMV, parvovirus B19, malaria
What are the different types of viral screen?
Antigen
Plasma antibodies (Seropositivity)
Nucleic acid amplification
Describe the features of Nucleic acid amplification technology
Introduced in the late 1990s
Many viruses replicate initially in lymph nodes or liver, so detection in plasma is not possible in early stages
PCR can amplify nucleic acid strands 10^9 -fold
How are blood products stored?
Red cells
- 4C (+/- 2C) in designated fridges
- Shelf-life 35 days
Platelets
- 22C (+/- 2C) in designated incubators (rockers)
- Shelf life 5 days
FFP
- 0.7 IU ml^-1 Factor VIII in 75% of unitsWhat is cryoprecipitate?
An extract rich in blood-clotting factor obtained as a residue when frozen blood plasma is thawed
How is cryoprecipitate produced?
A single unit of plasma is rapidly frozen at -30C
It is then slowly thawed at 4C - supernatant is removed (used for Fb preparation)
Left with a “slush” (Cryoprecipitate) that is rich in Fb, FVIII, FXIII, VWF
> 70 IU Factor VIII and 140mg Fb in 75 of units
Stored at
What are the various uses of red cells?
Anaemia:
Hébert et al. (1999) found patients fared better if a “trigger” of 70 mgml-1 was used rather than 100 mgml-1.
If patients are stable, asymptomatic DO NOT TRANSFUSE.
For elective surgery:
Treat anaemia (haematinics / EPO)
Stop anticoagulants / antiplatelet therapy if possible
Tranexamic acid to reduce bleeding
β-thalassaemia major, MDS, hypoplastic marrow
What are the various uses of platelets?
Platelet transfusion is used in patients who are thrombocytopenic or have disordered platelet function and who are actively bleeding (therapeutic use) or are at serious risk of bleeding (prophylactic use).
For prophylaxis, the platelet count should be kept above 5-10^9/L unless there are additional risk factors such as sepsis, drug use or coagulation disorders for which the threshold should be higher.
For invasive procedures (e.g. liver biopsy or lumbar puncture) the platelet count should be raised to above 50x10^9/L. For brain or eye surgery the count should be > 100x10^9/L.
Therapeutic use is indicated in bleeding associ- ated with platelet disorders. In massive haemorrhage the count should be kept above 50x10^9 /L.
Platelet transfusions should be avoided in autoimmune thrombocytopenic purpura unless there is serious haemorrhage. They are contraindicated in heparin - induced thrombocytopenia, thrombotic thrombocytopenic purpura and haemolytic uraemic syndrome
What are the uses of FFP?
Rare clotting factor deficiencies (no recombinant product available)
Multi-factor deficiencies (liver failure, DIC, warfarin overdose)
What are the uses of cryoprecipitate?
Specific FVIII-deficiency (if rFVIII not available)
VWD
Massive haemorrhage with low Hb or risk of circulatory overload
Fb concentration of 300 ml cryoppt = 1300 ml FFP
