One of several different systems of diagnosis in Chinese medicine. This system can be contrasted with San Jiao diagnosis, Four Level diagnosis, Eight Principles, and Zang Fu diagnosis. Six Channel diagnosis deals with invasion of the body by cold External Pathogenic Factors. It outlines how a pathogen invades the body from the exterior levels to the deep internal levels, stage by stage, how to diagnose and treat the disease at each stage, and how the natural untreated progression of the disease will eventually lead to death. Six Channel diagnosis was established in the classic book, the Shang Han Lun. The Six Channels — Tai Yang, Yang Ming, Shao Yang, Tai Yin, Shao Yin, and Jue Yin—are defined in more detail individually.