Symptoms are related to diagnoses in the way that they correlate with one another, states MedicineNet. Doctors use symptoms to create a likely diagnosis for illness or disease. Symptoms are subjective clues to a patient's underlying condition, and doctors interpret them to determine what tests may be necessary.
Both symptoms and signs are manifestations of a health condition, and health care professionals use both to decide what that condition may be, explains MedicineNet. Symptoms are subjective evidence, such as fatigue and pain, while signs are objective observations, such as a bloody nose. Symptoms and signs may indicate more than one possible diagnosis, so doctors compile a list of diagnoses and perform tests to eliminate possibilities and determine initial treatments.
A medical diagnosis is a health care professional's identification of a disease or illness, states MedicineNet. It also refers to conditions that cause a health problem, such as a malfunctioning intravenous line. The word originally meant the difference between two possibilities, but that meaning is closer to what modern doctors call a differential diagnosis. A differential diagnosis is a list of several possible diagnoses.
As of 2015, online symptom checking tools are available through companies such as MedicineNet, WebMD and Healthline. These tools identify conditions associated with particular symptoms. Healthline provides a list of common symptoms, and WebMD lists symptoms of common conditions.