THE AFL has finalised its guidelines for blood rule interchanges, advising clubs that players forced from the ground under the rule will still be allowed to return if their limit of 90 has been reached.

However, if a player is forced from the ground under the blood rule before a team has used its 90 rotations, they will need to reserve one to get that player back on the ground.

The tweaks to the rule follows confusion back in round three when North Melbourne forward Drew Petrie could not return to the ground after he was forced off with the blood rule in the dying minutes against Melbourne.

The AFL considered making all blood rule interchanges excempt from the cap of 90, but has settled on a tighter rule in making sure clubs reserve a rotation if they haven't reached their limit.

It means blood rule interchanges will not be treated in the same way as rotations for genuine medical reasons while clubs still have rotations up their sleeve.

"If the player has been forced off the field by the umpire under the blood rule prior to the cap being reached, the team should reserve one of its remaining interchanges should they wish for that player to return to the field," the League told clubs. 

If a player is returning to the field after the club has used its 90 rotations, he can replace any player and there is no need to reverse the initial blood rule interchange.