BACKGROUND: Guidelines for allogeneic transfusion emphasize minimizing use to avoid transmission of serious illness. However, there is little information on the risks associated from withholding transfusion.

STUDY DESIGN AND METHODS: A retrospective cohort study of patients who declined RBC transfusions for religious reasons was performed. This analysis was restricted to consecutive patients ≥18 years old, who underwent surgery in the operating room from 1981 to 1994 and had a postoperative Hb count of 8 g per dL or less. The primary outcome was defined as any in‐hospital death occurring within 30 days of the surgery. Secondary outcome was 30‐day mortality or in‐hospital 30‐day morbidity. Morbidity was defined as myocardial infarction, arrhythmia, congestive heart failure, or infection.

RESULTS: Of 2083 eligible patients, 300 had postoperative Hb counts of 8 g per dL or less. The study population was predominantly female (70.3%) with a mean age of 57 years (SD, ± 17.7). In patients with a postoperative Hb level of 7.1 to 8.0, 0 died (upper 95% CI, 3.7%), and 9.4 percent (95% CI, 4.4‐17.0%) had a morbid event. In patients with a postoperative Hb level of 4.1 to 5.0, 34.4 percent (95% CI, 18.6‐53.2%) died and 57.7 percent (95% CI, 36.9‐76.6%) had a morbid event or died. After adjusting for age, cardiovascular disease, and Acute Physiology and Chronic Health Evaluation II score, the odds of death in patients with a postoperative Hb level of ≤8 g per dL increased 2.5 times (95% CI, 1.9‐3.2) for each gram decrease in Hb level.

CONCLUSIONS: The risk of death was low in patients with postoperative Hb levels of 7.1 to 8.0 g per dL, although morbidity occurred in 9.4 percent. As postoperative blood counts fall the risk of mortality and/or morbidity rises and becomes extremely high below 5 to 6 g per dL.