Examples herein provide a method. The method includes applying an electrical potential difference over a blood sample in a testing cassette of a microfluidic device, the cassette including a microfluidic channel through which the blood sample flows. The method includes measuring, over a duration of time, an electrical signal passing through the blood sample as the blood sample flows from a first end and coagulates at a second end of the microfluidic channel to obtain a measurement function as a function of time. The method also includes correlating the measurement function to a characteristic of the blood sample.