Fluid mechanics of thin blood films to detect anemia and sickle cell disease

Anemia affects nearly two billion people worldwide, especially in low-income countries, while sickle-cell disease (SCD), which is genetically inherited, is prevalent in sub-Saharan Africa and India. These resource-constrained regions require cost-effective diagnostic screening, effective case monitoring, and treatment for the diseases. Existing devices screen for a single disease, requiring healthcare centers to stock multiple devices for diagnosing different diseases, thereby adding costs. Here, we present a rapid, cost-effective screening assay based on blood smear that utilizes viscosity measurements from a blood drop to aid in the simultaneous screening of anemia and SCD. The method is based on the fluid mechanics of thin films, where the blood smear length is controlled by a balance of viscous and surface tension forces. Viscosity below a threshold due to low hematocrit indicates severe anemia, while a significant viscosity increase due to stiffening of red blood cells upon blood deoxygenation is a marker for SCD. Our method exhibits exceptional sensitivity in detecting severe anemia and SCD based on smear lengths, rivalling that of commercial screening devices. A decrease in viscosity for SCD patients undergoing drug therapy allows for effective monitoring and personalized medicine, which is unique to the proposed test.