BackgroundBleeding events are associated with higher mortality rates in patients with cardiovascular diseases, including patients presenting with acute coronary syndrome (ACS) undergoing coronary revascularization. We aimed to determine whether a reduction in hemoglobin (Hgb) from pre‐ to postpercutaneous coronary intervention (PCI), with or without evidence of clinical bleeding, is a correlate of in‐hospital mortality for patients presenting with ACS who underwent primary PCI.MethodsWe divided 33816 consecutive patients with ACS who underwent PCI into three categories: (1) target group (defined as Hgb reduction without overt bleeding [n = 112]); (2) Hgb reduction with overt bleeding (n = 48); and (3) control group (defined as no Hgb reduction and no overt bleeding [n = 3156]). Hgb reduction was defined as a drop of >3 g/dL in Hgb value from preprocedure and postprocedure during the index hospitalization. The primary outcome was in‐hospital mortality. We used logistic regression to examine the relationship between Hgb reduction with and without bleeding and in‐hospital mortality.ResultsIn crude analysis, the Hgb reduction with overt bleed group had a higher in‐hospital mortality rate (16.7%) than the target (9.8%) and control groups (0.6%). Adjusted logistic regression estimates a 0.393 (95% confidence interval [CI]: 0.137, 1.869) odds ratio for in‐hospital death of the target group over the Hgb reduction with bleed group, and a 54.517 (95% CI: 2.07, >1000) odds ratio of the target group over the control group.ConclusionsIn patients presenting with ACS undergoing PCI, Hgb reduction with and without overt bleeding were both independently associated with in‐hospital mortality.