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3. Transfusion > IBTS - Virology Testing > Flashcards

IBTS - Virology Testing Flashcards

1
Q

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

A

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

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2
Q

How do we ensure transfusion safety?

A

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

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3
Q

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

A

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

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4
Q

Why are we concerned with the infectious window period?

A

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

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5
Q

What requirements do we have for our screening assays

A

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

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6
Q

Talk about the sensitivity of our assays?

A

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

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7
Q

How do we screen for viruses?

A

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

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8
Q

List the immunoassays we use

A

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

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9
Q

How does the chemiluminescent immunoassay technology work?
(5)

A

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

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10
Q

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

A

Acridinium-labelled conjugate

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11
Q

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

A

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

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12
Q

What might cause a false positive
(2)

A

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

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13
Q

Why do we test with two HIV assays

A

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

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14
Q

Write about HIV

A

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

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15
Q

Write about HIV screening in the IBTS

A

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

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16
Q

What is the window period for HIV screening

A

23 to 90 days after exposure

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

17
Q

What is the risk of HIV transfusion

A

1 in 6.5 million donations

18
Q

What is the eclipse phase?

A

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

19
Q

Write about Hepatitis B

A

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

20
Q

Why do we test for HBcore

A

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

21
Q

Write about HBV screening

A

HbsAg assay as well as an anti-Hbcore assay

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

22
Q

Talk about NAT HBV screening

A

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

23
Q

What is Hepatitis C (HCV)?

A

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

24
Q

Write about our HCV screening

A

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

25
Q

What is HTLV

A

Human T-lymphotropic virus

26
Q

Write about HTLV testing

A

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

27
Q

Write about CMV

A

CMV is an enveloped double stranded DNA virus

Only causes mono like disease in immunocompromised/neonates

28
Q

Who should receive CM neg

A

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

29
Q

How do we screen for CMV

A

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

30
Q

Talk about malaria testing

A

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

31
Q
A

3. Transfusion (14 decks)

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