1. A method for a portable computing device to read a reaction area on a test strip, which is located in a peripheral device placed over an image sensor and a light source of the portable computing device, the method comprising: providing light with the light source, wherein the peripheral device directs light from the light source to the reaction area; capturing an image with the image sensor, wherein the image includes the reaction area; and determining an analyte characteristic based on a color of the captured reaction area in the image.