Patent ID: 6855561

Claim:
A test device for determining the presence or absence of an analyte in a fluid sample, the test device comprising: a) a solid support; b) an intermediate piece bearing a mark thereon; c) a matrix defining an axial flow path, the matrix comprising: i) a sample receiving zone, at an upstream end of the flow path, that receives the fluid sample, ii) a label zone, on the flow path downstream from the sample receiving zone, comprising a label reagent that binds with the analyte in the fluid sample flowing through the label zone, and iii) an observation area, on the flow path downstream from the label zone, the observation area comprising a defined capture zone having an immobilized capture reagent that restrains the analyte, wherein the observation area comprises a material that is opaque in a dry state and transparent in a moist state and the mark on the intermediate piece is visible through the observation area when the observation area is in the moist state; wherein the intermediate piece is disposed between the matrix and the support, iv) the mark has a shape such that, in the absence of the analyte in the sample, a first symbol is displayed to represent a negative result, and v) the capture zone has a shape such that, in the presence of analyte in the sample and taken together with the first symbol, a second symbol is formed to represent a positive result.