A droplet-based microfluidic rheometer system and method of use for real-time viscosity monitoring of blood coagulation is disclosed. Droplets of blood samples are generated in a microfluidic rheometer, and the size of the droplets is highly correlated to the sample viscosity. The size of the droplets can be determined optically using an inverted light microscope and a camera or using electrodes. The microfluidic rheometer systems provides viscosity measurements in less than a second and consumes less than 1 μl blood or plasma over an hour period. The viscosity measurements may be displayed and transmitted to the Internet or cloud storage.