Example implementations relate to coagulation sensing. For example, a microfluidic chip for coagulation sensing may include a microfluidic channel, an outlet at an end of the microfluidic channel having an air interface, and an impedance sensor located within the microfluidic channel and within a particular proximity to the air interface, the impedance sensor to determine a stage of a coagulation cascade of a blood sample flowing through the microfluidic channel to the impedance sensor.