I've only seen a patient's chart fully include information from other health systems once, even when the systems use the same EMRs. Three of the local systems here use Epic. Still, Epic's care everywhere function mostly just shows hospital names of where else the patient has been, with no further information when you click on that section. There has to be a formal request made to allow a facility to access records from somewhere else, and it's almost never done.
The only times I've had info provided from other health systems have usually been during transfers, where the patient will come with a paper copy of the chart, which may or may not ever get uploaded into the EMR. Regardless, being uploaded is not an instant process, so most of the things that come from OSHs just get redone on arrival. Too much of a pain in the butt to dig through a 40 page paper document when you can just repeat the CT/XR/labs/whatever yourself and have the results in your EMR.
Besides, when paper charts get uploaded, they are uploaded as a document attachment. In other words, even uploaded, you still have to open and manually search through a 40 page document to find anything. They come up like .pdf files and are often not searchable with a ctrl-F. Labs/test results still do not appear in the results section with results done at the current facility. It's still easier just to redo everything so information is readily accessible.
Upon transfer, most of my patients cannot self-report. What the physicians are able to know comes from whatever the physician at the previous facility told the receiving one. It's entirely word of mouth. You really hope the physician at the previous facility didn't forget much. If the patient transferred overnight, this means waking the patient families up at 3 in the morning to ask them basic health history questions if receiving staff is still fuzzy about what exactly is in the patient's history - assuming the family knows anything about the patient's history, which a lot of them don't. If you're lucky, you learn that the patient takes a little blue pill for "the sugar."
Like anything else in healthcare, I'm assuming it's about protecting all the stupid, interfering 3rd parties' interests. More people make more money with five hundred different EMRs to pay for than if there was one national EMR system. Heaven forbid we go to one system... lots of business-type middle men would lose their jobs and patients wouldn't have tests repeated just for convenience and would be able to save some money, which would clearly be horrible.
No concrete proof of any of that, by the way, I'm just a cynic.
