The effects of blood transfusion on red blood cell distribution width in critically ill patients: a pilot study

Red blood cell distribution width (RDW) is a measure of anisocytosis, generally used in the differential diagnosis of anemia. Recently, RDW was associated with increased mortality in critically ill patients. Red blood cell (RBC) transfusions are potential confounders on RDW values interpretation. The aim of this study was to analyze the changes in RDW after RBC transfusion in intensive care unit (ICU) patients.

This was a prospective, observational study including patients admitted to ICU requiring 1 RBC unit. We analyzed RDW values of the patients at four study points: before RBC transfusion (T1), immediately after transfusion (T2), 24 hours after transfusion (T3), and 48 hours after transfusion (T4). We also collected laboratory data from donors and RBC units. Changes of RDW (ΔRDW) were computed as the difference between baseline RDW value and RDW at each time point after transfusion.

We enrolled 36 patients. RDW values increased after transfusion (p < 0.001 at all points vs. baseline), with the highest level at T3. At T3, 34 of 36 patients (94%) had an abnormal RDW value (vs. 26/36, 72%) at baseline (p = 0.023). The maximum ΔRDW for each patient was moderately correlated with the difference between mean corpuscular volume (MCV)_donors and MCV_patient (r = 0.478, p = 0.005). Subgroups analysis showed that the maximum ΔRDW was greater in patients with baseline MCV lower than 80 fL or higher than 100 fL (n = 7) or baseline RDW of more than 14.5% (n = 19).

RBC transfusion significantly increased RDW values. This intervention should be accurately reported in the studies evaluating the prognostic role of RDW.