System that enables urine testing in a home environment. A user may apply a urine sample to a card containing multiple tests, and capture an image of the card using a phone; an analysis system executing on the phone or in the cloud may analyze the image and determine test results. The test card and analysis system may compensate for variability in lighting conditions and time of exposure to the urine sample, which are difficult to control in a home environment. The test card may contain fiducial markers of known colors; the analysis system may adjust colors in the captured image based on appearance of these markers. Color adjustments may also compensate for nonuniform lighting across the card. The card may also contain time indicators that change appearance over time after urine is applied, and the analysis system may use these indicators to calculate the time of exposure.