A sample test method, microfluidic device, and test device efficiently and accurately compensates for interference of an interfering substance present in a sample using optical measurement without addition of a separate reagent for detecting the interfering substance. The sample test method includes: measuring an optical characteristic value of a target substance present in a sample; measuring an optical characteristic value of an interfering substance present in the sample; and determining a concentration of the target substance for which interference of the interfering substance is compensated for based on the optical characteristic value of the interfering substance.