"To have a diagnosis" means that a medical professional has identified and determined the specific illness or condition that a person is suffering from. Full definition
These participants were not currently using alcohol or illicit substances and did not have diagnoses of dementia or other neurological problems. (sciencedaily.com)
We engage in confidential therapeutic work with people who have diagnoses like schizophrenia, bipolar disorder and serious depression. (shine.ie)
This may perhaps be due to less variability in the sample as all children have a diagnosis of ADHD. (link.springer.com)