A fluid sensor comprises a formed plastic body and a reagent. The body has a top face with an integral first surface. The body also has a bottom face opposed to the first surface and a sidewall that extends from the periphery of the top face. The first surface is adapted to accept a fluid sample. The reagent is disposed on the integral first surface and causes a color change detectable on the bottom face when the reagent reacts with an analyte in the fluid sample.