TS2

Question 1

Why do we transfuse blood?

Answer 1

• 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.

Question 2

Where are red cells used?

Answer 2

Acute blood loss
Anaemia in critical care
Chronic anaemia
Peri-operative transfusion

Question 3

Where are platelets used?

Answer 3

Bone marrow failure
Platelet function disorders
DIC
Autoimmune thrombocytopenia
NAIT (Neonatal alloimmune thrombocytopenia) 
Massive transfusion

Question 4

Where is plasma used?

Answer 4

Factor deficiencies
DIC
TTP (Thrombotic thrombocytopenic purpura)
Surgical bleeding

Question 5

Who can donate blood?

Answer 5

Normal healthy donors aged 17-70 (60 if first time)

Question 6

Who is excluded from donating blood?

Answer 6

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

Question 7

How many people give blood?

Answer 7

6% of the population

Question 8

In 2004 a new rule was introduced that people who had received a transfusion themselves can’t give blood.

Why was this?

Answer 8

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.

Question 9

Describe the blood preparation process

Answer 9

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.

Question 10

Describe the process of Leukodepletion

Answer 10

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)

Question 11

Which countries routinely leukodeplete blood?

Answer 11

UK
Ireland
France
Portugal

Question 12

Why does the USA not routinely filter blood?

Answer 12

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.

Question 13

What are the advantages of Leukodepletion?

Answer 13

Reduces risk of viral and prion infection

Reduces risk of immunological complications

Question 14

What are the disadvantages of Leukodepletion?

Answer 14

Cost
Hypotensive episodes from bedside filters
“Red Eye” Syndrome

Question 15

What are the 3 methods for viral inactivation of blood products?

Answer 15

Solvent detergent (works for plasma)
Metheylene blue (works for plasma)
Psoralens (S-59) (works for platelets)

Question 16

Describe the features of the solvent detergent method for viral inactivation of blood products

Answer 16

Disrupts lipid envelope of HIV and hep B, hep C viruses
Ineffective against non-lipid coated viruses (hep A,
parvovirus B19)

Question 17

Describe the features of the methylene blue method for viral inactivation of blood products

Answer 17

Generates ROS when exposed to white light, damages

DNA and RNA and prevents viral replication

Question 18

Describe the features of the psoralens (s-59) method for viral inactivation of blood products

Answer 18

Binds to DNA and RNA - rendered irreversible by UVA

Question 19

What are blood donations screened for?

Answer 19

Obligatory testing
- hep B, hep C, HIV-1, 2, syphilis, HTLV-I, II

Sometimes tested
- CMV, parvovirus B19, malaria

Question 20

What are the different types of viral screen?

Answer 20

Antigen
Plasma antibodies (Seropositivity)
Nucleic acid amplification

Question 21

Describe the features of Nucleic acid amplification technology

Answer 21

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

Question 22

How are blood products stored?

Answer 22

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 units

Question 23

What is cryoprecipitate?

Answer 23

An extract rich in blood-clotting factor obtained as a residue when frozen blood plasma is thawed

Question 24

How is cryoprecipitate produced?

Answer 24

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

Question 25

What are the various uses of red cells?

Answer 25

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

Question 26

What are the various uses of platelets?

Answer 26

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

Question 27

What are the uses of FFP?

Answer 27

Rare clotting factor deficiencies (no recombinant product available)
Multi-factor deficiencies (liver failure, DIC, warfarin overdose)

Question 28

What are the uses of cryoprecipitate?

Answer 28

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