Correcting a High Without Stacking

High readings need correcting, and the most common way people cause a low is by correcting too eagerly.

The problem is called stacking. Rapid-acting insulin takes about fifteen minutes to start and peaks at one to two hours, but it keeps working for around two to four hours in total. If you correct, see little change after forty minutes, and correct again, you now have two doses working at once — and the combined effect arrives later, often as a low.

So the discipline is to take a correction, then wait out the insulin's action time before considering another. Knowing your own insulin's duration is what makes this concrete rather than a rule of thumb.

Correction doses should come from a factor your team has worked out for you, not from guesswork about how high the number looks.

One thing that is not optional: check for ketones if your reading is high, particularly at 250 mg/dL or above, or if you are unwell. In Type 1 a high reading with ketones is a different situation from a high reading alone, and it needs urgent attention rather than another correction and a wait.

Finally, look for the cause. A high that follows a specific meal is a dose problem. Unexplained highs across a day can mean an infection, a failed injection site or a pump problem, or insulin that has been spoiled by heat.