The phrase "conclusive diagnosis" means that a decision or judgement has been made based on enough evidence and information, allowing for a final and certain determination of a medical condition or problem. Full definition
Terminal Illness involving conclusive diagnosis of an illness that is expected to result in the death of the insured person within 12 months. (securenow.in)
Tom hoped to hear a conclusive diagnosis, an anatomical explanation for his troubles and the rehabilitation strategy. (discovermagazine.com)
Laboratory work is ongoing and a conclusive diagnosis is not yet in. (sciencemag.org)