While anemia is a significant risk factor for poor outcomes in patients with heart failure (HF), it is not in defined guidelines for HF assessment. B-type natriuretic peptide (BNP) is a marker for diagnosis and management of patients with HF. We determined the incidence of anemia in patients with HF and the relationship between BNP and hemoglobin (Hgb) levels in patients with and without HF. Results from the Breathing Not Properly Multinational Trial consisted of 1,586 patients presenting to the emergency department (ED) with dyspnea. Because renal insufficiency is a confounding variable for BNP, patients with a creatinine of >or=2.0 mg/dL were excluded. The remaining data were evaluated from 620 non-HF patients (337 M, 283 F) and 547 HF patients (299 M, 248 F). The New York Heart Association (NYHA) HF classification and ejection fraction by echocardiography were assessed for HF patients. Blood was tested for Hgb, BNP, and creatinine. Using World Health Organization criteria for anemia, we observed that HF patients in NYHA class III or IV had lower mean Hgb levels (12.5 g/dL, P < 0.05) and a higher incidence of anemia (48.2%, P < 0.05) than did HF patients in class I or II (13.4 g/dL and 33.9%, respectively). There was no correlation between Hgb and log BNP for females without HF or the aggregate of all HF patients. In contrast, a significant inverse correlation was observed for males without HF (P < 0.001). Although there were differences in the BMI, age, and estimated glomerular filtration rate (eGFR) versus Hgb observed in this group, the log BNP correlation remained significant after multivariate analysis. A significant inverse correlation for log BNP and Hgb were also observed for diastolic (EF >or= 50) HF (P < 0.05) that was also not accounted for by the BMI, age, or eGFR. The presence of anemia is associated with worsening HF at ED presentation. For males without HF and diastolic HF patients of both genders, a low Hgb may be a confounding variable toward increasing BNP. Among systolic HF patients, the presence of a low hemoglobin concentration is not a factor in the interpretation of BNP results.