An eGFR blood test is used whenever there is suspicion of a kidney disease. This is usually the case in patients who are suffering from diabetes or from hypertension for a prolonged period of time.
In the case that your APP file doesn't open, it is highly likely that you do not have the correct software application installed on your PC to view or edit APP file extensions. If your PC opens the APP file, but it's the wrong application, you'll need to change your Windows registry file association settings. In other words, Windows is associating APP file extensions with the wrong software program.
It's also possible that you have the correct application on your PC, but .vcs files aren't yet associated with it. In this case, when you try to open a .vcs file, you can tell Windows which application is the correct one for that file. From then on, opening a .vcs file will open the correct application.