Microfluidic analysis of blood has potential clinical value for determining normal and abnormal erythrocyte deformability. To determine if a microfluidic device could reliably measure intra- and inter-personal variations of normal and oxidized human red blood cell (RBC), venous blood samples were collected from repeat donors over time. RBC deformability was defined by the cortical tension (pN/μm), as determined from the threshold pressure required to deform RBC through 2–2.5 μm funnel-shaped constrictions. Oxidized RBC were prepared by treatment with phenazine methosulphate (PMS; 50 μM). Analysis of the control and oxidized RBC demonstrated that the microfluidic device could clearly differentiate between normal and mildly oxidized (20.13 ± 1.47 versus 27.51 ± 3.64 pN/μm) RBC. In vivo murine studies further established that the PMS-mediated loss of deformability correlated with premature clearance. Deformability variation within an individual over three independent samplings (over 21 days) demonstrated minimal changes in the mean pN/μm. Moreover, inter-individual variation in mean control RBC deformability was similarly small (range: 19.37–21.40 pN/μm). In contrast, PMS-oxidized cells demonstrated a greater inter-individual range (range: 25.97–29.90 pN/μm) reflecting the differential oxidant sensitivity of an individual's RBC. Importantly, similar deformability profiles (mean and distribution width; 20.49 ± 1.67 pN/μm) were obtained from whole blood via finger prick sampling. These studies demonstrated that a low cost microfluidic device could be used to reproducibly discriminate between normal and oxidized RBC. Advanced microfluidic devices could be of clinical value in analyzing populations for hemoglobinopathies or in evaluating donor RBC products post-storage to assess transfusion suitability. Am. J. Hematol. 88:682–689, 2013. © 2013 Wiley Periodicals, Inc.