We encourage caregivers to test their cats on a regular basis. Unquestionably, home testing is the best way to insure your diabetic cat is in safe numbers. Even a well regulated cat can throw you a curve ball and numbers will be lower than expected. As an example, my kitty was one that liked to keep me guessing. She could start the day at 400, drop to the 40s, and be back to the 400s by her next shot time. (Obviously I'm using US numbers -- or 22 to 2.5 to 22.) If I hadn't gotten that spot check, I would have been increasing her dose versus finding out that she needed a dose reduction.
At the minimum, you want to get a test prior to each and every shot so you know numbers are in a safe range prior to giving an insulin injection. You also want to get at least one test during both the AM and PM cycles. If you look at the spreadsheets that are attached to our signatures, you'll see that people vary in how often they test. I was a testaholic. I also had a very unpredictable cat and I like data. There are times when you need to test frequently. Those are times when numbers are running low and you need to monitor to make sure that your cat is responding to your intervening with food. Then there's the rest of the time when you don't need to be testing often.
We tend to take a different approach then your vet. We want to see cats regulated so their numbers put them below renal threshold (roughly 200 or 11). Diabetes is tough on the kidneys and kidney disease is a common problem as cats age. Hence doing our best to get numbers below 200 or in normal range (50 - 120 or 2.8 - 6.7). Even better is if we can get a diabetic cat into remission. Vets get nervous with lower numbers since not that many caregivers will agree to home test. Home testing is the only way to insure your cat is safe -- something we can't say frequently enough!
As Wendy noted, Lantus does best when you give the same dose at each shot time. Lantus is a depot-type of insulin and any time your change the dose, it has an effect on the depot. Given that you're changing the dose at each shot time, the depot never has a chance to stabilize. You might want to take a look at the sticky notes on the
Lantus board to get more information on Lantus and how it works.