BACKGROUNDThere is considerable variation in disease behavior among patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 . Genomewide association analysis may allow for the identification of potential genetic factors involved in the development of Covid-19. METHODSWe conducted a genomewide association study involving 1980 patients with Covid-19 and severe disease (defined as respiratory failure) at seven hospitals in the Italian and Spanish epicenters of the SARS-CoV-2 pandemic in Europe. After quality control and the exclusion of population outliers, 835 patients and 1255 control participants from Italy and 775 patients and 950 control participants from Spain were included in the final analysis. In total, we analyzed 8,582,968 single-nucleotide polymorphisms and conducted a meta-analysis of the two case-control panels. RESULTSWe detected cross-replicating associations with rs11385942 at locus 3p21.31 and with rs657152 at locus 9q34.2, which were significant at the genomewide level (P<5×10 −8 ) in the meta-analysis of the two case-control panels (odds ratio, 1.77; 95% confidence interval [CI], 1.48 to 2.11; P = 1.15×10 −10 ; and odds ratio, 1.32; 95% CI, 1.20 to 1.47; P = 4.95×10 −8 , respectively). At locus 3p21.31, the association signal spanned the genes SLC6A20, LZTFL1, CCR9, FYCO1, CXCR6 and XCR1. The association signal at locus 9q34.2 coincided with the ABO blood group locus; in this cohort, a blood-group-specific analysis showed a higher risk in blood group A than in other blood groups (odds ratio, 1.45; 95% CI, 1.20 to 1.75; P = 1.48×10 −4 ) and a protective effect in blood group O as compared with other blood groups (odds ratio, 0.65; 95% CI, 0.53 to 0.79; P = 1.06×10 −5 ). CONCLUSIONSWe identified a 3p21.31 gene cluster as a genetic susceptibility locus in patients with Covid-19 with respiratory failure and confirmed a potential involvement of the ABO blood-group system. (Funded by Stein Erik Hagen and others.

Berzuini et al report the observation that nearly half of patients with COVID-19 tested at their blood center had a positive direct antiglobulin test (DAT). However, eluates did not react with any test cells but did react with red cells from other patients with COVID-19 that were DAT negative. This suggests that COVID-19 may modulate the red cell membrane and present novel antigenic epitopes.

Summary In 1999, we implemented an automated platelet cross‐matching (XM) programme to select compatible platelets from the local inventory for patients refractory to random donor platelets. In this study, we evaluated platelet count increments in 40 consecutive refractory patients (8·3% of 480 consecutive platelet recipients) given 569 cross‐match‐negative platelets between April 1999 and December 2001. XM was performed automatically with a commercially available immunoadherence assay. Pre‐, 1‐ and 24‐h post‐transfusion platelet counts (mean ± SD) for the 569 XM‐negative platelet transfusions containing 302 ± 71 × 109 platelets were 7·7 ± 5·5, 32·0 ± 21·0 and 16·8 ± 15·5 × 109/l respectively. Increments were significantly higher (P < 0·05, t‐test) than those observed in the same patients given 303 random platelet pools (dose = 318 ± 52 × 109 platelets) during the month before refractoriness was detected, when pre‐, 1‐ and 24‐h post‐transfusion counts were 7·0 ± 8·6, 15·9 ± 16·1 and 9·6 ± 12·8 × 109/l respectively. The cost of the platelet XM disposable kit per transfusion to produce 1‐h post‐transfusion platelet count increments >10 × 109/l was euro 447. This programme enabled the rapid selection of effective platelets for refractory patients, from the local inventory.

This study presents a flexible, quick, and economical method for complete genotyping of large donor cohorts for RBC alleles.

The diagnosis of autoimmune hemolytic anemia (AIHA) is based on a positive direct antiglobulin test (DAT), which is performed using various methods with different sensitivities. Recently, mitogen-stimulated (MS)-DAT was suggested to be able to identify latent anti-erythrocyte autoimmunity. Traditional methods (tube, microcolumn, and solid phase) and MS-DAT were compared in 54 consecutive cases of suspected AIHA, 28 idiopathic AIHA in clinical remission, and 12 difficult-to-diagnose cases of DAT-negative AIHA, and the results (all cases) were correlated with hematologic and hemolytic parameters. DAT tube was confirmed as the gold standard to diagnose AIHA since almost all positive cases showed hemolytic anemia and positive eluates; 10 out of 26 tube-negative cases were positive on microcolumn and solid phase antiglobulin tests, and 22 out of 26 using MS-DAT, although only half of them showed clear signs of hemolysis. Mitogen stimulation increased the amount of IgG bound to red blood cells in all groups; moreover, MS-DAT was the only positive test in 10 cases of AIHA, and mitogen stimulation facilitated the identification of autoantibody specificity in culture supernatants. We conclude that a battery of tests rather than a single test is useful for the diagnosis of AIHA, including MS-DAT as an additional test for selected cases, although the results have to be cautiously interpreted based on the overall clinical context.