It depends on what you call a "medical redshirt." Everyone gets 5 years to play 4, which is the key point people often lose sight of. A "redshirt" can be claimed any year where the athlete hasn't met the minimum number of games to count as a season. The reason doesn't matter. It could be due to injury, transferring, or being passed up on the depth chart.
@illini80 is correct that it is automatic; nothing has to be submitted to the NCAA (not sure about to the conference).
I think you might be thinking of what is often called a "medical hardship waiver." That is when a player appeals for a sixth year of eligibility due to some hardship (I don't think it has to be medical, but that is the most common), and that can only be requested after the initial five years of eligibility have expired. And, yes, Tracy Abrams received such a waiver. I don't believe the NCAA uses any of these terms I've placed in quotes, by the way, so there is plenty of confusion as to the meaning of terms.