Red Blood Cell Mechanical Fragility Test for Clinical Research Applications

Red blood cell (RBC) susceptibility to mechanically induced hemolysis, or RBC mechanical fragility (MF), is an important parameter in the characterization of erythrocyte membrane health. The rocker bead test (RBT) and associated calculated mechanical fragility index (MFI) is a simple method for the assessment of RBC MF. Requiring a minimum of 15.5 mL of blood and necessitating adjustment of hematocrit (Ht) to a "standard" value (40%), the current RBT is not suitable for use in most studies involving human subjects. To address these limitations, we propose a 6.5 mL reduced volume RBT and corresponding modified MFI (MMFI) that does not require prior Ht adjustment. This new method was assessed for i) correlation to the existing text, ii) to quantify the effect of Ht on MFI, and iii) validation by reexamining the protective effect of plasma proteins on RBC MF. The reduced volume RBT strongly correlated (r = 0.941) with the established large volume RBT at matched Hts, and an equation was developed to calculate MMFI: a numerical estimation (R²  = 0.923) of MFI if performed with the reduced volume RBT at "standard" (40%) Ht. An inversely proportional relationship was found between plasma protein concentration and RBC MF using the MMFI-reduced volume method, supporting previous literature findings. The new reduced volume RBT and modified MFI will allow for the measurement of RBC MF in clinical and preclinical studies involving humans or small animals.