Pre-transfusion Testing

Question 1

What is the difference between NAT and Serology testing?

Answer 1

Serology tests are looking for antibodies in the blood. An example of a TTI (infectious disease screening) serology test is an ELISA. This is a very sensitive and specific test that relies on the donor having made ana antibody against a specific pathogen - though these can have very long window periods.

A Nucleic Acid Test on the other hand is specifically testing for viruses and is therefore a highly sensitive discretionary test. As opposed to serology testing these actually measure the presence of the pathogen. This reduces the window period by detecting low levels of viral genetic material soon after the infection but before antibodies have been produced.

Question 2

What is NAT and how is it performed?

Answer 2

The test works by directly amplifying the and detecting viral RNA or DNA. This involves three stages:

1. Sample pooling and extraction of nucleic acid:
   Cost effective, amount in pool depends on site (usually 6-8 samples,
   but for HIV pool up to 24). If pool is negative, all are negative, if it is
   positive it means at least one in the pool is positive and all must
   be retested.
2. RNA/DNA amplification using PCR and specific primers for the disease
   in question.
3. Amplicon detection:
   Identifying whether viral nucleic acid is present