Association between the amount of blood drawn and changes in hemoglobin and hematocrit levels in ICU patients. A prospective cohort study.

Abstract

Introduction: Iatrogenic anemia is a common complication in Intensive Care Unit (ICU) patients, largely attributed to repeated diagnostic blood draws throughout a typical workday in these units. This continuous loss, particularly the volume discarded prior to sample collection, may lead to a progressive decline in hemoglobin (Hb) and hematocrit (Ht), increasing the need for transfusions and the risk of associated complications.
Objective: This study aimed to analyze the association between the total volume of blood drawn, including both the volume used for laboratory testing and the discarded volume, and the variations in Hb and Ht levels in critically ill patients.

Methods: A prospective, analytical, and longitudinal cohort study was conducted with 34 adult patients admitted to a tertiary-level ICU for at least 48 hours, without active bleeding or prior transfusions.

During follow-up, daily records were kept of the volumes of blood drawn for analysis, the pre-sample discarded volumes, and the corresponding Hb and Ht values.
Results: The results showed a significant decrease in both parameters during ICU stay. Although no statistically significant differences were found when comparing blood volumes drawn for analysis above or below 14 ml/day, a notable reduction in Hb and Ht was observed when the discarded blood volume exceeded 10 ml/day. This suggests that the pre-sampling discard has a greater clinical impact and is a determining factor in the development of iatrogenic anemia during hospitalization.

ROC curve analysis identified a 9.5 ml/day cutoff for discarded blood volume, with good

sensitivity and specificity for predicting ≥20% reductions in Hb and Ht.
These findings are consistent with previous studies and reinforce the need to establish

blood conservation strategies in this patient population.
Conclusion: The findings of this study indicate that reducing the volume of blood discarded during sample collection is essential to lowering the incidence of iatrogenic anemia in ICU patients. A significant association was found between the amount of blood drawn — especially the discarded portion — and the decrease in Hb and Ht. These results provide useful evidence to optimize blood extraction protocols and support the implementation of pediatric collection tubes, closed-loop reinfusion systems, and rationalized test ordering.