Use of the Microfluidic Impedance Red Cell Assay (MIRCA) in Sickle Cell Disease

• The Microfluidic Impedance Red Cell Assay (MIRCA) is a reproducible assay with readouts that correlate to sickle cell disease severity.

• We propose using MIRCA to measure RBC deformability at clinic visits to monitor SCD complication risk and need for therapeutic optimization.

In sickle cell disease (SCD), red blood cells (RBC) are poorly deformable, even under normoxia. With deoxygenation, deformability of sickle RBCs is further reduced due to polymerization of hemoglobin S (HbS). Rigid, poorly deformable sickle RBCs block microvasculature, causing ischemia, pain, and organ damage. The Microfluidic Impedance Red Cell Assay (MIRCA) can mechanically measure RBC deformability, providing occlusion index under normoxia (NOI) or hypoxia (HOI) as readouts. We analyzed RBCs from 68 adult and 34 pediatric SCD patients using the MIRCA. Higher HOI and NOI were positively associated with markers of inflammation, hemolysis, RBC density, older age, and severe SCD genotypes (HbSS/ Sβ0). Each 1% higher NOI across individuals was associated with a 6.3% higher incidence of acute complications per year. Individuals with chronic complications in the past year had a 3.1% higher median NOI than those without chronic complications. Individuals on chronic transfusion therapy (CTF) exhibit a subpopulation of poorly deformable RBC that is captured by the MIRCA, but not by a commercially available device that also measures RBC deformability, the LoRRca. In vitro addition of voxelotor or osivelotor to samples from individuals on CTF improved the deformability of these endogenous RBC. Longitudinally collected NOI and HOI values in HbSS individuals were stable, with a median percent point change of 13.3% and 15.7%, respectively. MIRCA can be used in combination with clinical laboratory tests to monitor RBC deformability as a biomarker of clinical status at routine clinic visits and included in clinical trials of disease modifying agents.