The phrase "to diagnose the disease" means to determine or identify an illness or medical condition that someone has, usually by examining their symptoms or conducting medical tests. Full definition
A special blood test that measure the hormones produced by the adrenal glands will help diagnose this disease in ferrets. (smallanimalchanel.com)
She's currently working on new molecular technologies to map the human immune system to help diagnose diseases. (businessinsider.com)
As might be expected, this marriage of biology and technology is also designed to find new ways of diagnosing the disease, monitoring its progression and delivering drugs to fight it. (scientificamerican.com)