We all know what diabetes means , at least the word diabetes mellitus [there is also a different disease : diabetes insipidus]

Vocabulary: https://www.thefreedictionary.com/diabetes

Diabetes: a passing through (referring to the excessive  urination), from diabainein to pass through.

Mellitus means sweet. In the past [Chinese] physicians diagnosed diabetes by checking if ants were attracted by the [sweet] urine of a patient with diabetes, therefore the mellitus [sweet] No referral necessary from your doctor!