Infective Endocarditis and Excessive Use of B− Blood Type Due to Surgical Treatment—Is It Only a Local Problem? LODZ-ENDO Results (2015–2025)

<b>Background/Objectives</b>: Infective endocarditis (IE) remains a rare but increasingly complex condition, posing significant challenges for cardiologists and cardiac surgeons. Blood groups from the ABO/Rh system have been associated with susceptibility to various diseases, including infections and bacterial colonization tendencies. However, data on the distribution of ABO/Rh blood types among IE patients are lacking. We hypothesized that the prevalence of ABO/Rh blood types among IE patients differs from their frequency in the general population. This study aimed to assess the distribution of ABO/Rh blood types in the LODZ-ENDO database in comparison to general populations. <b>Methods</b>: LODZ-ENDO is a single-center retrospective study conducted in a tertiary cardiology and cardiac surgery facility serving 2.35 million residents. All consecutive patients with confirmed IE hospitalized between 1 January 2015 and 1 October 2025 were included. Clinical data and ABO/Rh blood types were collected and compared with national population data using Fisher's exact and chi-square tests. <b>Results:</b> A total of 329 patients with IE were analyzed (median age 61 (41-68) years; 69% men), of whom 227 underwent cardiac surgery. Overall ABO/Rh distribution differed significantly from the general population (<i>p</i> = 0.033), driven by a tendency to an overrepresentation of B- (LODZ-ENDO 5.2% vs. Poland 2%; OR 2.88; 95% CI 1.17-7.29; <i>p</i> = 0.03; power 0.89; <i>p</i>(adj) = 0.23). Considering regional demographics and blood use (≈3 units per surgery), this represents an excess annual use of 1.9 B- units, equal to 0.23% of regional B- reserves, with additional indirect depletion of O- blood. Based on WHO data, if this overrepresentation exists elsewhere, IE-related surgeries could consume 0.2-1.3% of national B- stocks in smaller European countries such as Malta, Iceland, Luxembourg, Cyprus, Estonia, Lithuania, Latvia, and Slovenia. <b>Conclusions:</b> This, probably the first report of B- blood type overrepresentation in IE indicates disproportionate use of a rare blood group, highlighting the need for targeted blood management strategies, especially near specialized cardiac surgery centers.