Higher levels of D-dimer, LDH, and ferritin, all have been associated with the poor prognosis of COVID-19. In a disease where there are acute inflammation and compromised oxygenation, we investigated the impact of initial hemoglobin (Hgb) levels at Emergency Department (ED) triage on the severity and the clinical course of COVID-19. We conducted a cross-sectional study on 601 COVID-19 patients in a COVID-19 national referral center between 13 and 27 June 2020. All adult patients presented at our hospital that required admission or hotel isolation were included in this study. Patients admitted to the intensive care unit (ICU) had a lower initial Hgb than those admitted outside the ICU (12.84 g/dL vs. 13.31 g/dL, p = 0.026) and over the course of admission; the prevalence of anemia (Hgb < 12.5 g/dL) was 65% in patients admitted to ICU, whereas it was only 43% in non-ICU patients (odds ratio of 2.464, 95% CI 1.71-3.52). Anemic ICU patients had a higher mortality compared with non-anemic ICU patients (hazard ratio = 1.88, log-rank p = 0.0104). A direct agglutination test (DAT) for all anemic patients showed that 14.7% of ICU patients and 9% of non-ICU patients had autoimmune hemolytic anemia (AIHA). AIHA patients had significantly longer length of hospital stay compared with anemic patients without AIHA (17.1 days vs. 14.08 days, p = 0.034). Lower Hgb level at hospital presentation could be a potential surrogate for COVID-19 severity.