Recent developments in electrowetting-on-dielectric (EWOD) technology have expanded the possibilities for testing methods and investigation of blood. This work evaluated the development of necking geometry of whole blood on an EWOD-based digital microfluidic (DMF) platform. This was achieved by performing tensile tests on whole blood on an EWOD-based device, thereby inducing necking. A time-invariant method was used to evaluate the deformation of the tested dilutions, using minimum neck width and neck radius as two characteristic parameters of the necking geometry. Experiments were performed on blood diluted with phosphate-buffered saline (PBS) at dilutions of 1:20 and 1:10 by volume. Parameter measurements were obtained by recording microscope video of on-chip tensile tests and extracting the necking profile. Neck radius and neck width are obtained from the extracted necking profile and evaluated to compare results. Results from tensile tests on blood at different dilutions showed an exponential decrease in neck radius as neck width decreases. A four-parameter exponential model was fit to the collected data, showing that the 1:20 dilution had a higher neck radius to neck width ratio than the 1:10 dilution over a neck width interval of 0.3 mm to 1.7 mm, suggesting a viscosity effect on the necking geometry. The results demonstrate that the concentration of blood influences the necking profile when deformed under tension that is applied by electrowetting forces.