Introduction: Approximately 25% of the patients with hospital acquired anemia (HAA) develop moderate to severe HAA during hospitalization. This is related to an increased risk of prolonged stay, readmission and mortality. The primary aim was during one year to characterize a population with very frequent phlebotomies based on a university hospital in the Capital Region of Denmark and the related general practitioners Material and methods: We conducted a retrospective cohort study using administrative data on phlebotomies from 1 January 2019 to 31 December 2019 analyzed at a university hospital. Results: A total of 203,811 patients had 10,083,207 requisitions and 1,373,013 tubes. One percent, 1985 patients, had an extreme of frequent phlebotomies >60 tubes and formed the basis for the study population. The study population was significantly older as compared to the excluded patients (<60 tubes) (mean 65.7 vs. 51.6 years, p <.001).The likelihood of hemoglobin decrease per 100 mL blood drawn were calculated at four levels of decreases: Hemoglobin decrease of 2 mmol/L (adjusted OR; 95%; 2.03, CI 1.79–2.31), hemoglobin decrease of 3 mmol/L (adjusted OR; 95%, 1.36, CI 1.28–1.45), hemoglobin decrease of 4 mmol/L, (adjusted OR; 95%, 1.27, CI 1.19–1.35) and hemoglobin decrease of 5 mmol/L, (adjusted OR; 95% 1.22, CI 1.13–1.31). Conclusions: Moderate to severe HAA occurred in a limited group with excessive many phlebotomies. It was a worrisome trend that the frailest patients had the highest risk of developing HAA.