Abstract: A miniaturized, vented capillary channel test strip device for estimating the concentration of an analyte in a fluid is disclosed. The channel transports analysis fluid through interior capillary space defined by the plastic casing of the device. The casing is preferably manufactured by flow injection molding. The capillary channel includes a reaction and a wicking component. Movement of analysis fluid from sampling to reaction to wicking site is enabled by a gradient of capillary force. The gradient is generated by a differential in surface/volume ratio between reaction and wicking component. The reaction component is comprised of a thin reagent film embodying the reactive chemicals, as well as a rehydrating polymer. The polymer absorbs a defined volume of analysis fluid. When the analysis fluid is whole blood, the polymer absorbs blood plasma. Surprisingly and uniquely, cellular component of blood is wholly removed from the reagent film surface by the gradient of capillary force.