The invention relates to a microfluidic device comprising at least one test channel (2) comprising an upper test channel section (6) with an upstream end and a sampling region (4) at its upstream end and at least one reference channel (12) comprising an upper reference channel section (16) with an upstream end and a sampling region (4) at its upstream end. The test channel and the reference channel have a merging region (7) downstream to said upper test channel section and a common downstream channel section (8). The merging region (7) and the common downstream channel section (8) are arranged such that a reference liquid flowing from the upper reference channel section into the merging region will block a test liquid flow in the upper test channel section when said test liquid flow has not yet reached the merging section. The microfluid device may preferably be used for detecting change of flow properties e.g. due to agglomeration, agglutination rpr viscosity change in a liquid preferably selected from the group of water, urine, blood, and blood plasma.