Sex Differences in Anemia and Red Blood Cell Transfusions Among General Internal Medicine Inpatients

Background: Epidemiological data from the general population have shown that women have lower hemoglobin values compared to men. Previous research on surgical patients showed that women were significantly more likely to receive red blood cell (RBC) transfusions compared to men in the peri-operative period due to multiple factors including the application of absolute transfusion thresholds. Sex differences in RBC transfusion frequencies have not been well studied in non-surgical settings. Here we investigated sex differences in anemia and in RBC transfusion frequencies in patients admitted to General Internal Medicine (GIM) wards.

Study design and methods: This was a retrospective cohort study using de-identified electronic patient data from all patients admitted to the GIM wards from the emergency department across 4 different hospitals between 2010 and 2017, who had at least 1 CBC test during their admission. Patients with multiple hospital admissions during the study period, those who were pregnant, those who underwent surgery during the admission, and those transferred to or from another service besides GIM during their admission were excluded. Severity of anemia was stratified using the WHO sex-specific quantitative thresholds for hemoglobin: mild anemia (110 to 119 g/L in women and 110 to 129 g/L in men), moderate anemia (80 to 109 g/L in both men and women) and severe anemia (lower than 80 g/L in both men and women).

Results: The study cohort consisted of 51,073 inpatients (24,666 men and 26,407 women). The median hemoglobin at the time of admission was significantly higher (p < 0.001) in men (median 135 g/L, IQR 31) compared to women (median 127 g/L, IQR 25). The prevalence of moderate and severe anemia was significantly higher (p < 0.001) in female inpatients (56%) compared to males (44%). The proportion of patients who received RBC transfusions during their admission was not significantly different (p = 0.36) between men (49%) and women (51%). There was no significant sex difference (p = 0.28) observed in the median hemoglobin prior to RBC transfusions between men (median 68 g/L, IQR 10.5) and women (median 68 g/L, IQR 11). The number of patients with pre-transfusion hemoglobin less than 70 g/L, the commonly used threshold for transfusion in the in-patient setting, was not significantly different (p = 0.91) between men and women. However, among the patients with hemoglobin < 70 g/L, a significantly lower proportion (p < 0.001) of women (82%) received RBC transfusions compared to men (91%).

Conclusions: In a large cohort of GIM inpatients, we observed significantly higher prevalence of moderate and severe anemia in women compared to men. While there was no sex difference in overall RBC transfusion frequencies in this inpatient population, there was a lower proportion of women receiving RBC transfusions compared to men in the subgroup of patients with hemoglobin less than 70 g/L.