Delaying the measurement of a complete blood count (CBC) for 6 to 24 hours after red blood cell transfusion remains a common practice in hospitals worldwide, despite the absence of strong physiological or empirical justification. This narrative review summarizes the available clinical evidence comparing early versus delayed post-transfusion evaluation of hemoglobin (Hb) and hematocrit (Hct) levels in adult patients. Studies conducted in the United States, Spain, Colombia, and Thailand, including more than 290 hemodynamically stable, non-bleeding adults, assessed Hb and Hct levels at different intervals ranging from 15 minutes to 24 hours after transfusion. Across all studies, early post-transfusion measurements showed no statistically significant differences when compared with delayed testing, demonstrating that Hb and Hct values stabilize rapidly within 15 to 60 minutes following transfusion. These findings refute the traditional assumption that several hours are required for equilibration. Implementing early CBC testing provides accurate results, enables prompt assessment of transfusion efficacy, reduces unnecessary delays in clinical decision-making, and improves hospital workflow efficiency. Therefore, early measurement of Hb and Hct is safe, reliable, and cost-effective in stable adult patients.