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.
For example, you can have all .jpg image files open using one app, and .bmp image files open using a different app. The default you choose will only apply to your account and won't affect other accounts on this PC. On the defaults page, tap or click Choose default apps by file type, or Choose default apps by protocol.