Hi Erica, welcome!
I believe that the "do not shoot below" number for a new diabetic is 150. I'm not sure what to tell you, since you have no data on Harry's use of Lantus. My suggestion would be to skip (as per the protocol):
"Q4.4. My cat's pre-shot level was way below the usual value. Should I give the injection?
A4.4. There's no hard and fast rule, but if you don't have data on how your cat responds to insulin, here are some general guidelines. Below 150 mg/dl (8.3 mmol/L), don't give insulin. Between 150 and 200 (8.3-11.1 mmol/L), you have three options: a.) give nothing; b.) give a token dose (10-25% of the usual dose); c.) feed as usual, test in a couple of hours, and make a decision based on that value. Above 200 (11.1 mmol/L) but below the cat's normal pre-shot value, a reduced dose might be wise. In all cases, if you are reducing or eliminating insulin, it's wise to check for ketones in the urine. Above the normal pre-shot value, give the usual dose, but if the pre-shot value is consistently elevated, it's a good idea to schedule a full glucose curve to see whether a change in dose or insulin is appropriate. In most cases, the target "peak" value should not be below 100 mg/dl (5.6 mmol/L), and for some cats it might be higher. Keep in mind that these are general guidelines, and they should be personalized to your own cat's reactions to insulin. If your experience is that your cat does not became hypoglycemic with a dose which is close to her usual, then your experience should be your guide."
When you skip a shot you can feed. It is only when you are stalling when you are not supposed to feed, because food will influence the bg number. Do spend some time today reading the "Stickies". They are full of important information about how to proceed with Lantus.
Welcome to you and Harry,
Ella & Rusty
p.s. What dose will you be giving?