Background COVID‐19 convalescent plasma (CCP) is plasma collected from individuals who have recovered from SARS‐CoV‐2 infection. The FDA Emergency Use Authorization restricts use of CCP to high‐titer units only. The purpose of this study was to determine if donor ABO blood group was associated with SARS‐CoV‐2 antibody response, and subsequent qualification as high‐titer CCP. Methods All CCP donations collected from April 21, 2020 to September 1, 2020 were included. The Abbott ARCHITECT semi‐quantitative chemiluminescent microparticle immunoassay was used to assess IgG antibodies to the nucleocapsid protein of SARS‐CoV‐2. Units with a S/C value ≥4.5 were considered high titer. Results A total of 232 CCP donations were evaluated. There were no significant differences in the distribution of sex, age, and interval from symptom resolution to donation by ABO blood group. The mean SARS‐CoV‐2 IgG antibody S/C value was significantly lower in blood group O donations (3.6), compared to blood group A (5.0) donations ( p < .001). There was no difference in antibody response between the other blood group pairings. Blood group O donations resulted in a lower percentage of high‐titer units (35%), compared to blood group A (60%), B (58%), and AB (65%) donations. Conclusion Blood group O donations were found to have significantly lower levels of SARS‐CoV‐2 IgG nucleocapsid antibodies compared to blood group A donations and were less likely to produce CCP units that qualified as high titer. These findings may aid donor recruitment to promote availability of high‐titer CCP to meet patient needs.

Background: There is a small but growing number of thrombotic thrombocytopenic purpura (TTP) cases attributed to immune checkpoint inhibitor therapy, with nivolumab and ipilimumab therapy being the most frequently described in the literature.Study Design and Methods: This report evaluates the course of a patient with a history of metastatic adenocarcinoma of the lung who developed TTP following treatment with the PD-1 inhibitor Pembrolizumab. The patient was treated with six sessions of therapeutic plasma exchange and appeared to be in remission. Exacerbation occurred 4 days later, and seven more sessions of plasma exchange were performed along with four total doses of Rituximab, and a steroid taper with monitoring of platelet counts and ADAMTS13 activity.Results: His platelet count recovered to a peak of 318,000 UL with an ADAMTS13 activity of 77% at the time of discharge. The patient has been following up regularly for outpatient testing with no TTP relapse as of the completion of this report.Discussion: This is one of a few cases of Pembrolizumab-associated TTP reported in the literature with successful complete remission following treatment. Plasma exchange in this setting may be an especially beneficial therapeutic intervention because of the removal of both the anti-ADAMTS13 antibody as well as the immune system upregulating anti-PDL1 monoclonal antibody with replacement of ADAMTS13 from donor plasma. Longer duration of plasma exchange and monitoring for normalization of ADAMTS13 levels in addition to platelet count before cessation of treatment may improve durable remission rates in this entity.