Hi Carmine,
The food will start to raise your blood sugar around 15 minutes after you eat. If you're trying to ensure that you took enough insulin and prevent a high blood sugar, try checking again between 30 to 45 minutes and again after about an hour and a half from when you ate.
Here's a link, too, to how to determine your insulin-to-carbohydrate ratio for meals.
-Ginger
It depends on the insulin that you are taking, and the time it takes for that insulin to "peak."
If I'm not worried about being very high, I wait the full two hours to test. My doctor has always told me that Humalog takes two hours to fully peak. If I wait, I can be sure that my blood sugar is probably relatively stable, so I won't take too much insulin as a correction.
If I really feel like I spiked, I will test earlier, about an hour or and hour and a half after. Usually I can tell if I will need extra insulin.
And of course, if I feel low, I always test right away and have a snack. :)
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