IBTS - Nucleic Acid Testing Flashcards
How many people receive BTs every week?
Over 1000 every week
How many donations do we need every week to fulfil requirements?
3,000
How many donations so we get every year?
140,000
Write about using serology and NAT testing to test our donors
NAT and serology complement each other to detect viral infections
We use Alinity analysers in serology but Panther analysers in NAT
What do we test for in NAT?
HIV-1/2
HCV
HBV
HEV
Selective WNV testing
Is HIV RNA or DNA
RNA
Is HBV RNA or DNA
DNA
Is HCV RNA or DNA
RNA
Is HEV RNA or DNA
RNA
Is WNV RNA or DNA
RNA
Why use NAT
NAT detects very low levels of viral RNA or DNA
They are qualitative tests -> either positive or negative (not great for donor as it doesn’t say how much of an infection they have)
What is meant by selective West Nile Virus testing?
Only test on donors who have travelled to a risk area
What is the newest assay introduced
Hepatitis E assay
When can NAT not detect a virus?
Cannot detect viral infections during the eclipse phase (when stored in liver/lymph)
What sample type is used for NAT
Plasma or serum
What is the window period
The time between acquiring an infection and when it can be detected using serological markers (antibodies)
What is the main benefit or NAT?
Detects viral RNA or DNA early in the development of infection (during the window period) before antibodies are detectable
Comment on RNA replication versus DNA replication
RNA replicates rapidly -> substantial increase in viral load <5 days after infection -> doubling time only a few hours e.g. HIV @ 20 hours
DNA replicates slower -> can take several weeks to reach detectable levels e.g. HBV which has a doubling time of 2-3 days
Write about the combination of HBV NAT testing and HBV serology testing
HBV DNA can detect early infection (3 to 12 weeks)
HBV DNA + HBsAg detects acute infection (3 to 12 weeks)
HBV DNA + anti-Hbc total - detects chronic infection (DNA might not be detectable)
What proves to be the biggest risk to donors and why
HBV due to its very slow doubling time making it very difficult to detect
Low DNA levels are undetectable during the window period or are often below the limit of detection by the assay
Low DNA also seen during chronic HBV infections which can also be HBsAg negative -> may only have anti-Hbc positive serology
What is a chronic HBV infection also called?
Occult HBV infection
What Assay method is used
Ultrio Elite Assay Methodology
What are the main steps to the Ultrio Elite Assay method?
- Sample prep -> DNA/RNA extraction
- RNA/DNA target amplification
- Detection of amplified target
How is DNA/RNA amplified using the Panther?
Transcription mediated amplification (TMA)