P1622: antiphospholipid antibodies in convalescent plasma of donors recovered from mild covid-19

Background: High prevalence of antiphospholipid antibodies (APLA) in patients with COVID-19 has been reported. A meta-analysis concluded that APLA were detected in nearly half of hospitalized patients with COVID-19, and even higher prevalence was found in patients with severe disease.These reports raised questions about the true prevalence and clinical impact of APLA on disease course, long term complications and the prothrombotic influence of COVID-19 convalescent plasma (CCP) transfused to COVID-19 patients. Aims: To evaluate the prevalence of APLA in CCP samples collected from otherwise healthy donors who recovered from mild COVID-19. Methods: CCP was collected from volunteer donors in two time periods (September 2020-January 2021 [early period] and April- May 2021 [late period]). The study was approved by the local ethics committee and all donors and controls signed informed consent. The study was supported by a grant from the Laboratory Research Fund, Shamir Medical Center. Convalescence was supported by studying serum anti COVID-19 antibodies (Ab): Anti- N (nucleocapsid protein) Ab during the early period, and anti- S (Spike1 protein) Ab during the late period.Anti- N Ab were tested by a chemiluminescent immunoassay. Positive results were defined as sample/cutoff (S/CO) ≥1.4. Anti-S1 Ab were tested using ELISA. Results ≥ 50 arbitrary units per milliliter (AU/ml) were considered positive. Plasma samples were tested for APLA: Lupus anticoagulant (LAC)testing was performed using dilute Russell Viper Venom Time (dRVVT) and Silica Clotting Time (SCT). Results were reported as normalized ratios. APLA IgG, IgM and anti-β2-glycoprotein IgG, IgM antibodies were detected using an ELISA method and reported as SGU u/ml or SMU u/ml. Results: Table 1 summarizes demographic data and laboratory results of plasma collected from donors. Plasma from 10 healthy volunteers were used as controls (8 women, median age 29 years [range 20-42]). None of the participants had an history of thrombosis. Early period CCP donors were significantly older compared to late period CCP donors, and approximately 80% of donors were male. Two donors had elevated APLA values and 5 had elevated normalized LAC SCT ratio, for a total prevalence of 6%. LAC was positive in the late period while APLA were found in the early period. All controls were negative for LAC and 9 were APLA negative. One woman had an elevated APLA anti-β2GP1 IgM (40.1 SMU u/ml).There was no association between anti-SARS-CoV-2 antibodies titer and the presence of LAC / APLA. Image:Summary/Conclusion: Our results demonstrate low frequency (6%) of APLA / LAC in plasma collected from donors who have fully recovered from mild COVID-19.The low frequency of APLA/LAC can be explained by the mild COVID-19 disease prior to plasma donation or the rapid disappearance of autoantibodies after the acute disease. The presence of LAC in the plasma of late period CCP donors and APLA in the early period donors can be explained by the changed in SARS-CoV-2 viral variants between the two time periods (wild type alpha and non-alpha variants in the early and late periods, respectively).The age of plasma donors in early CCP period was older than the age of those who donated in late period, reflecting the fact that the alpha variant was more common in elderly people during the early pandemic or that there was a careful selection of CCP donors during the course of the pandemic. The fact that convalescent donors had no thromboembolic disease at the time of plasma collection and the low prevalence of APLA/LAC in this cohort, reassures the safety of CCP use.