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.
Once the default app is SET, the application will open. It might however open with some error-message like 'FILE CANNOT BE OPENED' or 'ERROR WHILE OPENING FILE'. Don't worry, the application is SET as default successfully. You can verify by clicking BACK BUTTON on that application and going back to Default App Manager.