Because of the recent technological advances in modern medicine, every doctor seems to have become a superspecialist. They have a lot of expertise in their particular domain, but they often don't have a holistic picture of the entire patient. While they know a lot about the particular organ system in which they specialise , they don't care about the other body systems which the patient also has. Patient care starts getting fragmented, and this is why your diabetic specialist has no interest or clue as to what your nephrologist is doing.
This is why it's so important that patients learn to become experts on their diseases. Otherwise you will end up getting completely messed up because of the crossfire between them. Tests will be needlessly repeated; multiple drugs will be prescribed, which may interact with each other and cause side-effects; and the lack of coordination will mean your medical bills will grow exponentially.
The patient needs to become the CEO of his personal medical team. You have to be decision-maker, medical researcher, record keeper, medical secretary, coordinator, and financial manager. All the doctors you go to need to trusted team-players he pays to help you to achieve your goal - treat your disease as efficiently as possible, so that you can get well soon.
Often you will find that one specialist has no clue what the other one is doing. They are completely focused on the organ which they have an interest in , as a result of which there is no one who's in charge of coordinating all the efforts and putting all the doctors together in one page.
This problem is going to get worse as we start living longer. Most older people have multiple chronic illnesses, but there is no one doctor who is responsible for their overall medical care - it's all over the place, because each specialist is myopic , and is not only interested in dealing with his area of special interest ( after all, this is why he is called a specialist !)
This is why patients need to step up. While they don't need to become doctors themselves, they need to understand exactly what each doctor is doing and why. They need to make sure that every doctor knows exactly what's happening.
The good news is that there are many useful tools which you can use to help you do this. Prepare a one-page summary before the visit, so your doctor gets an overview of what is going on; create a timeline which describes your story and your progress; design an Excel spreadsheet or a project management chart , which will help all the doctors to make sure they're on the same page when treating you. There are also lots of online tools and apps which you can use. And if you get stuck, you can also employ a patient advocate
to help you through the process.