IBTS - Virology Testing

Question 1

What are the minimum legal requirements that blood be tested for?

Answer 1

Individual donations must be tested for antibodies to:
- HIV type 1/2
- hepatitis C virus
- hepatitis B surface antigen (HbsAg)

Question 2

How do we ensure transfusion safety?

Answer 2

Careful selection of donor -> travel history, high risk activity etc
Laboratory screening
Viral inactivation (SD plasma) and leukodepletion
Appropriate Blood Use
Haemovigilance
- Transfusion reaction reporting
- Guidelines
- Audit and review

Question 3

What are the main sources of risk in the transfusion service
(6)

Answer 3

The infectious window period
Immunosilent infection (no antibodies)
Variants/mutations of known agents
Laboratory error
New agents for which no test is available
Unknown agents

Question 4

Why are we concerned with the infectious window period?

Answer 4

The blood donor is infectious but has not yet developed antibodies or a detectable viral load

Question 5

What requirements do we have for our screening assays

Answer 5

High sensitivity and specificity
High throughput and automated
Rapid turnaround time
High level of traceability
Low cost

Question 6

Talk about the sensitivity of our assays?

Answer 6

Need highly sensitive assays that dont need to be extremely specific
- we want to detect the smallest amount of viruses
- not worried about typing the virus

Question 7

How do we screen for viruses?

Answer 7

We use the Abbott Alinity system
Chemiluminescent immunoassay technology
They determine the presence of specific antigens and antibodies

Question 8

List the immunoassays we use

Answer 8

HIV Ag & Ab
Anti-HCV
HbsAg
Anti-HBcore
Syphilis
Anti-HTLV I/II
Anti-CMV IgG

Question 9

How does the chemiluminescent immunoassay technology work?
(5)

Answer 9

Paramagnetic particles are coated in recombinant viral antigen

These are used to capture virus specific antibodies in the donor sample

The mixture is washed

AHG/AHM acridinium-labelled conjugate is added to create a reaction mixture and incubated

Following a wash cycle, pre-trigger and trigger solutions are added and the resulting light emission is captured and measured

Question 10

What is the anti-human IgG/IgM labelled with in the immunoassays?

Answer 10

Acridinium-labelled conjugate

Question 11

How do we manage positive viral testing results?
(5)

Answer 11

Reactive samples are first duplicated
Any products which have a repeat reactive result are discarded
Samples are then referred to a reference lab
A follow-up donation is requested
The donor is notified and deferred for a speicific period of time depending on what virus has been detected
True positive donors are then offered medical counselling

Question 12

What might cause a false positive
(2)

Answer 12

Transient non specific reactions e.g. cross reacting antibodies e.g. flu vaccination programme

Reactivity that persists from sample to sample -> antibodies specific to a component of the assay e.g. anti mouse antibodies

Question 13

Why do we test with two HIV assays

Answer 13

HIV is a retrovirus with two primary types: HIV1 and HIV2

HIV1 is more virulent and relatively easily transmitted

HI2 is less transmissible and is largely confined to West Africa

Question 14

Write about HIV

Answer 14

HIV infects and kills CD4 lymphocytes

HIV infection is often asymptomatic

523 diagnoses of HIV in Ireland in 2018

Transmission through sexual contact, infected blood/blood products/IV drug use

Question 15

Write about HIV screening in the IBTS

Answer 15

Testing using both serology and NAT on all blood donations

CMIA detects the presence of HIV-1 p24 antigen

The test detects antibodies to HIV-1 and antibodies to HIV-2

Question 16

What is the window period for HIV screening

Answer 16

23 to 90 days after exposure

Inclusion of HIV1 p24 antigen has decreased the window period to approximately 15 days

Question 17

What is the risk of HIV transfusion

Answer 17

1 in 6.5 million donations

Question 18

What is the eclipse phase?

Answer 18

This is where the virus replication is restricted to tissue sites e.g. lymph nodes so there is no detectable viraemia

Question 19

Write about Hepatitis B

Answer 19

An infection which causes inflammation of the liver and can lead to cirrhosis

Most adults clear HBV within 6 months but infants can develop chronic infection

498 cases of HBV in 2018

Question 20

Why do we test for HBcore

Answer 20

0.4% of the Irish population are core positive - we want to detect these as well

Anti-HBcore was used to identify donors in later stages of infection or in those with latent infections

Question 21

Write about HBV screening

Answer 21

HbsAg assay as well as an anti-Hbcore assay

NAT was also introduced as it reduces the HBV window period to 20.6 days

Question 22

Talk about NAT HBV screening

Answer 22

It takes several weeks before the viral load reaches concentrations detectable by NAT

NAT is carried out to detect HBV DNA in serologically negative donors during the early stages of infection

Question 23

What is Hepatitis C (HCV)?

Answer 23

HCV is an infection which causes inflammation of the liver

About 25% of people with an infection will clear the virus within one year but 75% will develop chronic infection

474 cases in Ireland in 2019 -> mostly associated with IV drug use and migrants

Question 24

Write about our HCV screening

Answer 24

CMIA to detect anti-HCV
Window period is 56 days
NAT also used for HCV RNA which reduces the window period to 4.9 days

Question 25

What is HTLV

Answer 25

Human T-lymphotropic virus

Question 26

Write about HTLV testing

Answer 26

We test for HTLV type 1 and type II

Detectable from 41 to 65 days

Lecudepletion significantly reduces the risk of transmission as it is a cell associated virus

Not everyone does HTLV screening, some only test first time donors

Question 27

Write about CMV

Answer 27

CMV is an enveloped double stranded DNA virus

Only causes mono like disease in immunocompromised/neonates

Question 28

Who should receive CM neg

Answer 28

Pregnant women
Children <1
Children with immunodeficiencies
Bone marrow or stem cell transplant recipients
Solid organ transplant recipients

Question 29

How do we screen for CMV

Answer 29

We currently screen selected donations approximately 80% for CMV antibodies in order to have a supply of CMV- blood

Question 30

Talk about malaria testing

Answer 30

We have 2 screening assays for anti-malaria antibodies to allow donors who have ever been resident in a malaria endemic area for 6 months or more to donate