I've been on the other side of the table from this. I went through long bouts of heavy depression when I was younger. Sadly, I was one of those kids who did it for attention, not because my life was truly hard. I can honestly say that the best thing my mother ever did was call the police. I wasn't arrested per say, but I was institutionalized for a week on two different occasions. Being away from literally everything, family, friends, environment, can do more to relieve stress than talking once it gets to that level. I wouldn't wait till you're 98 percent sure. Honestly, if you're that sure it may be to late. If you're even 20 percent sure, just make the call. I know it's a hard thing, and you may feel awful, but if your friend doesn't thank you for it now they will eventually.