Introduction: Each unit of packed red blood cells (PRBCs) is expected to raise circulating hemoglobin (HGB) by approximately 1 g/dL. There are few data on modifiers of this relationship other than gender and body mass index (BMI).
Methods: We recorded HGB before and after PRBC transfusion in a retrospective cohort of 103 patients and a prospective cohort of 93 patients with subarachnoid hemorrhage (SAH).
Results: In the retrospective cohort, 48 of 103 patients were transfused, and in the prospective cohort, 56 of 93 patients were transfused. In both groups, lower pre-transfusion HGB was associated with a larger increase in HGB (P < 0.001) after correction for the number of units of PRBCs given. In the prospective cohort, lower pre-transfusion HGB was associated with a greater rise in HGB (P < 0.001) after correction for number of units of PRBCs given, gender, and BMI in repeated measures analysis. Pre-transfusion HGB explained an additional 12% of variance in the data (P < 0.001). In both cohorts, the magnitude of the effect was similar.
Conclusion: In patients with SAH, transfusion at lower HGB leads to a greater increase in HGB. Transfusion at lower HGB may be relatively more cost-effective, and this should be balanced against any potential benefit from higher HGB in SAH. One rather than 2 units of PRBCs are likely to be sufficient for most HGB targets after SAH, especially in patients with more severe anemia.