A medical diagnostic device for measuring an analyte concentration or property
of a biological fluid includes capillary flow channels to convey a sample of the
fluid from an inlet to a branching point, and then to a measurement area and, alternatively,
through a bypass channel to an overflow region. A first stop junction stops fluid
flow after it enters the measurement area. The bypass channel has a capillary dimension
in at least one direction. A second stop junction, in the bypass channel, has boundary
region that has a dimension that is greater in that direction and forms an angle
that points toward the branching point. With this construction, the second stop
junction initially prevents flow to the overflow region, but permits the flow after
the measurement area is filled. The device is particularly suited for measuring
coagulation time of blood.
