Hi Elise and extra sweet Max! Welcome to Lantus Land!
Just to add to Wendy's answer, if you get a pre-shot test that's 150 or below, you still don't exactly "Withold" insulin, but you do what we call "Stall".
When you stall, you
don't feed, and retest in 20-30 minutes to see if the numbers are rising. You don't want to feed him so you can be sure he's on the way up without the influence of food. (which is also why you should take up any food you have down for the 2 hours prior to pre-shot time).
During that "stall time", post here and ask for help. If you go to your first post of the day and edit the subject line, just add something like "Stalling..advice needed" so when people are scanning the board, they can see that you need help quickly.
Once you get more data on how Max reacts to insulin and food, that "no shot" number comes down, but there is rarely a time that we don't give any insulin at all.
If you post and ask for help, and nobody is available in that 20 minutes(or the board is down, or you have internet issues) you should have
Shooting and handling low numbers printed out somewhere where you can find it. On the refrigerator door is where mine are, and there's a copy in my "hypo kit" too.
Once again, welcome!