Anemia is an important determinant of heart failure and death after ST elevation myocardial infarction (STEMI). The frequency of anemia and its impact on these outcomes across the range of acute coronary syndromes (ACS), however, have not been defined.

This is a cohort study of 2310 patients with ACS stratified by quartiles of admission hemoglobin concentration [Hb]): Q1, <12.5 g/dL; Q2, 12.5-13.6 g/dL; Q3, 13.7-14.7 g/dL; Q4, >14.7 g/dL.

There were 29.7% of women and 23.2% of men who were anemic. Rates of STEMI increased across [Hb] quartile groups from 25.0% (Q1) to 35.5% (Q4) as rates of unstable angina decreased from 52.0% (Q1) to 40.7% (Q4) (P < .0005). Despite this, rates of left ventricular failure (LVF) were inversely related to [Hb] in all diagnostic groups, patients with unstable angina (Q1, 14.2%; Q4, 4.4%; P < .0005) showing a similar trend to patients with non-STEMI (Q1, 26.8%; Q4, 10.4%; P < .0005) and STEMI (Q1, 33.8%; Q4, 20.6%; P < .0005). The age-adjusted odds of LVF in Q4 compared with Q1 were 0.64 (95% confidence interval, 0.45-0.90). Inhospital cardiac mortality was 3.0% and was not influenced by [Hb].

Anemia is a common comorbidity in patients presenting with ACS, and it is a powerful independent determinant of LVF. The association with LVF occurs not only in STEMI but also in less severe diagnostic groups.