Final answer:
In the field of medicine, a secondary diagnosis code is used to provide additional information about a patient's condition during a particular encounter or treatment.
Step-by-step explanation:
In the field of medicine, the note that describes codes that are never first listed or principal diagnosis codes and are always additional codes is called secondary diagnosis code.
Secondary diagnosis codes are used to provide additional information about a patient's condition during a particular encounter or treatment. These codes are typically used to report comorbidities, complications, and other relevant diagnoses that are not the primary reason for the visit.
For example, if a patient with diabetes is admitted to the hospital for a broken leg, diabetes would be considered a secondary diagnosis code because it is not the primary reason for the hospitalization.