It means that more information is needed before a decision on his medical status can be determined.
It may be a request for additional medical records, it may be additional medical testing, it may be something as simple as the doctor forgetting to sign the form.
You don't need to do anything, you will be contacted by mail as to what you/he needs to do.
Or you can go into proactive mode and contact Larry Mullen instead of waiting.
Sometimes a test result (i.e. blood pressure or protein in urine) from the physcial exam may be out-of normal ranges, requiring a remedial medical test.
Sometimes the applicant indicates a "history of" something that requires DODMERB to investigate further (childhood allergies, for example) before they can make a final decision on the medical status of the candidate.
To add on to what others have said, don't be too alarmed. There are literally 29 pages of remedial codes in very small print so while I don't know the actual % of applicants who get remedials requested, I wouldn't be surprised if it was pretty darn high. Many of them are very minor, like verifying ortho work or whatever that just needs a doctor to sign a form and send back in.
You can Google "Dodmerb remedial codes" and get the whole list if you want to know what's coming your way.
The percentage of remedials is meaningless to the individual applicant. If we need more tests, consults, and/or information fro a particular applicant, we'll let them know. Again, this is all individually based