Talk:Karthus/@comment-4949668-20120326165143/@comment-77.236.25.91-20120326200156

First read the item description. It doesnt grant 400 dmg shield before lethal damage, it grants it before the magic damage that would leave you at less than 30% of your maximum health. If you are running away with 300 hp, it means that the shield must have been popped before and anyway no protection will be given to you.

To make this item block lethal damage Requiem, you would need i.e. a carry with 2500 maximum health and weak resistances, running away with 800 hp, and a late-game Karthus with 700 ap. Could happen sometimes, bot not very likely in general.