Diagnosis codes are numbers that doctors use to help them remember information about a person's health. They are used to record the healthcare services a person has received, and can also help doctors to better understand a patient's condition and provide better care. For example, a doctor may use a diagnosis code to understand why a patient has a particular symptom or to track the progress of a patient's illness over time. Diagnosis codes help to make sure that everyone is on the same page about what is happening with a patient's health.