The positive result of complement-dependent cytotoxicity crossmatch (CDC XM) may not constitute a contraindication to renal transplantation, unless it is mediated by IgM antibodies, particularly of the autologous type. The current work presents the evaluation of the frequency of reactive IgM antibodies in sensitized kidney patients in Poland and their influence on panel-reactive antibodies (PRAs) readout and allocation status.Results of PRA CDC assay with and without dithiothreitol were elaborated in 53 prospective recipients with historic PRA of ≥50%. Delta PRA (dPRA) was calculated. Retrospective analysis of the results in the context of age, sex, transplant number, and cause of end-stage renal failure was performed.Reactive IgM antibodies were detected in 81% of patients. Panel reactivity completely disappeared in 4% and in 51% of recipients PRA decreased by 2 to 77 percentage points. In 14 patients, PRA increased, and in 10, its level did not change. The allocation was altered in 36% of recipients. Priority status was lost in 8 and gained in 3 cases. Additional points for high sensitization were obtained in 1 and lost in 7 patients. dPRA was significantly greater in patients awaiting the first transplant compared with the second (P = .007) and third (P = .002). Higher dPRA was also symptomatic for autoimmune patients (P = .025).Reactive IgM antibodies affected PRA level and allocation in a considerable group of sensitized patients in Poland. Discrimination of IgM from IgG antibodies should be introduced to the recipient qualification algorithm.