Insulin: basal and bolus
The insulin story is more complicated. Our body uses energy all the time, even when we sleep, and there is a fairly constant rate of glucose being released at rest in the body every hour. So we need some insulin every fraction of an hour, at a certain “basal” rate. For us T1Ds, there is a special kind of convenient insulin, a slow-releasing, long-acting “basal” insulin, that we can inject every 12 or 24 hours and that will give us a fairly steady release into the bloodstream over that period of time.
On top of that “basal” rate, every time we eat, we are adding, soon afterwards, a lot of glucose to the blood, for which we need to inject insulin, otherwise all that glucose will just stick around in our veins and raise our BG. This insulin needs to act quickly, in order to follow the rate at which our meal turns into glucose in our blood. This short-acting insulin injection we call “bolus.” Bolus is a medical term that means a single dose of medicine delivered at once, such as a pill or an injection—-but for us T1Ds it is a word in daily use!
There are many different insulins, made by different manufacturers and for different uses. Insulins are injected or inhaled, and each type of insulin has a different speed of activation. In general, most people, when using multiple daily injections (“MDI”), use a basal, long-acting insulin that they inject every 12 or 24 hours, and a short-acting insulin that they use for bolus, either for meals or for BG corrections. This is how I started: when I left the hospital, I was supposed to take one injection of long-acting insulin per day, and one injection of short-acting insulin with each meal. This is probably how you are starting too. Whether you use Humalog, Novolog, or Fiasp, they all function as short-acting “bolus” insulins, just as Lantus, Levemir, and Basaglar act as long-acting “basal” insulins, so we will refer to them as such.
Treating a high
In the same way as we treat a low (hypoglycemia, or hypo) with carbs, we treat a high (hyperglycemia) with short-acting bolus insulin. For the low, we eat carbs—-for the high, we inject bolus insulin.
Growing up T1D 