Abstract: A test member suitable for use in a test device for testing of analyte concentration in a fluid to be applied thereto comprises a base member (2) having a working area (4) to which the fluid is to be applied, containing a reagent which is reactive to the said analyte to produce an electrical signal or a color change, and a non-working area (8) adjacent to the working area (4). The total thickness of the test member in at least a portion of the non-working area (8) is at least as great as the total thickness of the test member in the working area (4).