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Testing questions


The NHS Blood and Transplant Clinical Trials Unit is managing the convalescent plasma aspects of the REMAP-CAP and RECOVERY trials.

This page answers some of the common queries about testing convalescent plasma for these trials. 

What method/kit is used for the neutralising antibody assay?

We use microneutralisation test to measure Tissue Culture Infectious Dose (TCID). This assay is performed in a category 3 laboratory at Public Health England (PHE).

ERO E6 cells are infected with SARS-CoV-2 pre-incubated with a serial dilution of convalescent plasma.

Neutralising antibody titre is determined as the plasma/serum concentration that inhibits 50% of SARS-CoV2 growth.

What neutralising antibody assay is being used? The cut-off of 1/100 is very low.

Approximately 35-40% of convalescent plasma donations collected so far contain antibody titre 1:100 or higher.

It is important to note that in many countries this titre is determined with another assay - Plaque Reduction Neutralisation Test (PRNT) - and hence these numbers are not comparable.

Based on most previous literature, 1:100 obtained by microneutralisation test would correspond to approximately 1:300-1:400 obtained by PRNT.

How well correlated are your neutralising antibody results from two different assays?

Of the test assays that we have investigated most have a moderate or strong correlation with the neutralisation antibody results.

Can the devolved nations get access to the neutralisation assay to test potential donors?

We plan to share the data we have collected on assay performance with devolved nations (Scotland, Wales and Northern Ireland) and other blood operators internationally. 

We are already in discussion with colleagues across the devolved nations about this.

Do convalescent plasma donors undergo the same checks as usual blood donors? 

Yes.

How is the convalescent plasma being standardised for antibody concentration? 

Each donation will be tested, and there is a threshold antibody level which every donation must meet in order to be validated/added to stock.

The threshold level has been set based on previous research and will be regularly reviewed. 

There is variation and this is part of the rationale for splitting donations – so recipients receive units from different donors, giving them a better chance of receiving a good antibody dose. 

Contact us

Please email
NHSBTCustomerService@nhsbt.nhs.uk
if you have any further questions about testing.



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