The medical tricorder is a version of the tricorder designed for doctors, used to examine patients and diagnose injury and illness in the field.
Dr. McCoy carried a medical tricorder with a small detachable hand scanner that he passed over patients to read their condition, a design that continued into the 24th century. Doctors such as Beverly Crusher, Julian Bashir and the Doctor relied on later versions to take readings outside sickbay.
The device gives physicians the ability to assess vital signs, detect injuries and identify unfamiliar pathogens on an away mission, and it often provided the first clue that a crew member had been altered or infected.