Initiation of an analytical measurement procedure for blood

A distinctive optical signature permits a fluidic medical diagnostic device to measure an analyte concentration or a property of whole blood, particularly the coagulation time, only after first insuring that a whole blood sample has been introduced into the device. A suitable device has at one end a sample port for introducing a sample and at the other end a bladder for drawing the sample to a measurement area. By requiring a meter, used in conjunction with the device, to first detect the distinctive optical signature, a sample is drawn to the measurement area only if it is whole blood. In that case, a channel carries the sample from the sample port to the measurement area, and a stop junction, between the measurement area and bladder, halts the sample flow. The meter measures a physical property of the blood sample - typically, optical transmittance - after it has interacted with a reagent in the measurement area.