How to recognize installed ads block

Hello friends. I looked through several posts but didn’t find an answer. How can I recognize that admob ads are being blocked by ad blockers? At first I did a test, if the advertisement does not appear, with the block (failed to show), I made a message box appear asking the user to disable the blocker. But I know this is just an experiment, as the ad may not appear for several other reasons. Could you help me identify this blockage?

Nothing…no suggestions?