Influence of hematocrit detection methodology on transfusion practice

Introduction

Transfusions of allogeneic red blood cells (RBC) are associated with viral and bacterial infections, activation of inflammatory pathways, transfusion-related acute lung injury and transfusion-associated circulatory overload. To reduce and prevent such harmful consequences, a clear indication for transfusion of RBC is required. However, our clinical experience shows that the method of assessing hematocrit is of crucial importance when implementing a strict trigger-dependent transfusion practice with the aim of preventing unnecessary transfusions, especially in non-bleeding critically ill patients. The aims of the present study were therefore to compare two different hematocrit-assessing methods used in clinical routine and to determine whether the results obtained by these two methods would influence our RBC transfusion management.

Methods

A total of 50 patients treated on our ICU for at least 5 days in which daily blood counts including hematocrit analysis were performed were investigated (250 paired samples). Hematocrit was analyzed using our blood gas analyzer (ABLflex 800) located on our ICU and the routine method used by the central laboratory (ADVIA^® 2120). Post hoc, patients were grouped according to the predefined transfusion triggers (24% and 28%) used on our surgical ICUs for different illnesses.

Results

Bland–Altman analysis for repeated measurements showed a good correlation with a bias of +1.39% and two standard deviations were ± 3.12%. The 24% hematocrit group (n = 30) showed a correlation of r² = 0.87 and the kappa was 0.56; that is, 22.7% of the cases would have been differently transfused. In the 28% hematocrit group (n = 20) there was a correlation of r² = 0.8 and the kappa was 0.58; that is, 21% of the cases would have been differently transfused.

Conclusion

Despite a good agreement between the two methods with which hematocrit is determined in clinical routine, the calculated difference of 1.4% will substantially influence transfusion practice, resulting in erroneous RBC transfusion in approximately 21% of our patients. This, in turn, could endanger these patients. Consequently, the transfusion trigger used in clinical routine is strongly dependent on the used method of analysis and must be taken into account.