CD40LG and COVID-19: Among those assays performed by three or more EQA participants, two in-house assays (VNT, PRNT) and six commercial assays (Abbott – SARS-CoV-2 IgG II Quant, Beijing Wantai Biological – SARS-CoV-2 Ab ELISA, Euroimmun – Anti-SARS-CoV-2 QuantiVac ELISA IgG, Roche – Elecsys Anti-SARS-CoV-2 S, Vircell microbiologists – COVID-19 ELISA IgM+IgA and GenScript - SARS-CoV-2 Surrogate Virus Neutralisation Test Kit) correctly characterised all EQA samples in all laboratories that assessed these assays (Table 3).