Pre-Transfusion Testing

Question 1

What is the purpose of pre-transfusion testing?

Answer 1

Provide a blood component to a patient that will provide maximum benefit while minimising potential for harm

The end goal is for the clinician/scientist to be able to choose the most appropriate blood product from a safe, compatible donor and infuse it into a properly identified and thoroughly tested recipient

Question 2

What are the mandatory tests?

Answer 2

ABO and Rh D type
– Anti-A, anti-B, Anti-D (reverse typing)
– Antibody screen

Confirmation of known donors, result compared to historical computer record - BUT a BMT from a different match (not an issue) would cause you to start producing different blood group RBCs

For new donors (no historical record), grouping is performed twice, independently to allow a similar check. Both results must agree.

All blood donations are tested for:
– C,c,E,e,K
– High titre anti-A, -B
– Syphilis TpHA/TpPA

Question 3

What is Transfusion microbiology and what tests are mandatory?

Answer 3

This department is responsible for performing all MANDATORY
microbiology testing

Follow up of discrepant results with full liaison with independent reference laboratory

Investigation of suspected post-transfusion infection

Discretionary testing of donors with extra risk
- Performed based on evidence provided by donor, e.g. in a malaria endemic area 7 months ago

Transfusion transmitted infectious agents tested for must:
- have an asymptomatic phase – disease symptoms missed
at donation
- be able to survive in blood
- Route of transmission must be via blood
- Recipient must be susceptible to the disease

MANDATORY TESTS:

• Hepatitis B
- HBsAg (surface antigen) mandatory in UK (in early stage of
infection this is not as sensitive as core antigen test)
- window period is 24 weeks
- HBc (core) only performed on donors with a history of
hepatitis or body piercing/tattoos
- window period is 6 weeks
- NAT test can pick up viral DNA in 2 weeks

• Hepatitis C
- Detected using ELISA specific for antibodies to HCV and NAT
- Window period for HCV RNA is 1-2 weeks
- window period for antibodies is 2 months
- If ELISA is positive but NAT is negative, indicates that the patient
had a previous HCV infection but has cleared it

• HIV I and II
- Detected using ELISA specific for antibodies to HIV I and II and NAT
- positive ELISA’s are re-tested in duplicate
- If either duplicate is reactive, specimen is reported as repeatedly
reactive and must be confirmed by Western Blot
- only if this is positive is the sample reported as HIV+
- antibodies have a 4-12 week window period
- viral load has a window period of 2-3 weeks

• HTLV I and II
- detected using ELISA to detect antibodies to HTLV

• Syphilis
- Readily inactivated by refrigeration for 72h - therefore usually
only transmitted by fresh blood or platelet concentrates
- Incubation period varies from 4 weeks to 4.5 months - average
is approx. 9-10 week
- But antibodies usually remain in the blood many years after the
infection has gone - a positive test for syphilis often relates to a
historic infection

• Hepatitis E*

All tests must comply with national standards of performance, using approved kits

Each run must include independent standards to
prove compliance
• How do we decide what to test for?

Question 4

What is the definition of a window period?

Answer 4

From infection through to the point at which we can detect the infection in the laboratory

Question 5

What is the definition of an incubation period?

Answer 5

From infection through to the point at which clinical symptoms appear

Question 6

What is the definition of an eclipse period?

Answer 6

Time from entry into the cell until the time when you can see new virus in the cell

Question 7

What are discretionary tests?

Answer 7

Malaria:
- Can survive storage of blood at 4°C for more than a week
- Testing indicated by donor questionnaire
- Transmission does still occur in the UK despite careful taking of travel
histories prior to donation
- Testing is performed using serological evidence of malarial antibodies

West Nile Virus
- Most cases of WNV are not serious and many people have no
symptoms/mild flu-like symptoms, e.g. muscle aches, fever
- Testing indicated by donor questionnaire and is done by ELISA

Chagas’ disease:
- Testing indicated by donor questionnaire and is done by ELISA

Prion Diseases:
- Creutzfeldt-Jakob disease (CJD) is one of a group of diseases
that affect the CNS
- caused by a PRION – prion replication stands as an exception to
the central tenet of biology – do not contain nucleic acids but can
still self-replicate!
- It is non immunegenic and has no genetic material so ELISA
and NATs don’t detect it
- vCJD (from mad cow disease) can be transmitted from person
to person via medical products/instruments
- vCJD may infect a patient via blood – to date four confirmed cases
- Exclude all donors who have received blood in the UK
since BSE became present in the UK food chain
- All blood components are LEUKODEPLETED
- ‘club 96’

Cytomegalovirus (CMV):
- 50% of UK donors are seropositive (rate inc with age)
- Only 3-12% of donor units transmit the virus – no test to determine
which seropositive donors are infectious
- Selective screening of donor units to meet the demands patients:
– Interuterine transfusions
– Neonates
– Pregnant women
- Leukodepleted units do not transmit CMV, but if anti-CMV testing
is already in place it should continue

Question 8

What is bacterial monitoring of platelets?

Answer 8

Platelet units are stored in an agitated state at 22°C

This is ideal growth conditions for bacterial cultures

As a result platelets have a very short shelf-life
– 5 days
– 7 days with appropriate bacteriological monitoring

Main sources of bacteria are:

• Contamination with bacteria present on skin at time of donation
• Donor bacteraemia
• Contamination present in blood banks

BacT/ALERT screening:
- Automated Testing System
- Two aliquots taken from platelet unit; aerobic culture and
anaerobic culture
- Unit quarantined for 36 hours
- Unit released to hospital
- Testing of original aliquots continues for the shelf-life of the
product
- Positives are discarded/recalled
- If transfused, patient must be treated accordingly
- Approx. 50 platelet units per year (or approx one per week) are
flagged-up nationally across all NHSBT Centres as initial reactive
- Positive sample must be sent to the National Bacteriology Testing
Laboratory for confirmatory testing and phenotypic identification.
- The info obtained may be used to inform treatment of an infected
recipient and may allow monitoring of infection trends.
- Bacterial phenotyping is performed by isolation, culture, staining and
biochemical methods.