Adjusting insulin doses to prevent hypoglycemia

It depends on when the hypoglycemic episode happens. A basal insulin dose that is too high raises the risk of hypoglycemia during the night, in the morning on an empty stomach and sometimes between meals. A meal dose that is too high causes hypoglycemia two or three hours after you eat [1].

Repeated corrections are the third cause, and the easiest to miss. Correction doses add up on top of each other, and their combined effect sometimes shows up later [2]. The time at which hypoglycemia occurs is the best clue to the dose that needs changing.

By a telling pattern. Your blood glucose falls during the night or three hours after a meal, with no obvious cause. You feel you need to eat so as not to slip into hypoglycemia, and if you skip a meal, your blood glucose keeps falling on its own.

It is checked together with your doctor, through a period of supervised fasting or by carefully reading the sensor reports [3]. A correct basal insulin dose keeps blood glucose almost flat when you are not eating or exercising, including during sleep [1]. If the line keeps going down, the basal insulin dose may be too high.

It is the amount of insulin left over from an earlier dose that is still working. A rapid-acting insulin analog usually works for three to five hours, with its peak action within the first two hours [4]. Pumps and many apps can display this amount if they are set up correctly [5].

It is a very useful number when you are thinking about a correction. If your active insulin is high, remember that a new correction adds on top of it. Ignoring it can explain many episodes of hypoglycemia that seem to have no cause [5].

Their effects overlap, as the figure below shows. Each correction works for several hours. Its effect on blood glucose can sometimes show up slowly, and it is tempting to give another small dose of insulin. In the end, 2–3 times more insulin than you really need at that moment can build up in your body.

The result usually shows up a few hours later, as a rapid fall in blood glucose that is hard to stop [2]. The practical safety rule is to wait until a correction has almost fully taken effect before giving the next one. Automated systems do this calculation on their own, which explains part of their protection against hypoglycemia [6].

Yes. This ratio tells you how many grams of carbohydrates one unit of insulin covers. If the value you use gives too much insulin for the meal, your blood glucose falls two or three hours after you eat [1].

The pattern is easy to recognize because it shows up at the same meal, again and again. The ratio can differ between morning and evening and it changes over time, especially in children and teenagers [7]. It is changed together with your doctor, based on several days of observation [8].

Yes. The sensitivity factor tells you how much one unit of insulin lowers your blood glucose. If the value you use is lower than the real one, every correction will contain too much insulin [9].

The effect shows up after corrections, not after meals. Insulin sensitivity changes with body weight, physical activity and age [7] [8]. That is why this number is rechecked regularly, just like the insulin-to-carbohydrate ratio used for meals.

Yes, more than most patients expect. Absorption is fastest from the abdomen, slower from the arm and slowest from the thigh and the buttock. An injection that goes into muscle by mistake is absorbed much faster and raises the risk of hypoglycemia [10].

The second problem is areas thickened by fat, which appear where you always inject in the same spot. Absorption from lipohypertrophy lumps is unpredictable, sometimes very slow and sometimes sudden [11]. These lumps occur in almost two thirds of patients who use insulin every day [12]. Unexplained hypoglycemia is much more common in people who have lipohypertrophy lumps [13].

A few simple measures protect you:

• Correct rotation of injection sites, which is the strongest protective factor [12].
• A new needle for every injection, because reusing the same needle also raises the risk [12].
• Short 4 mm needles, which lower the chance of an injection into muscle [11].
• Checking your injection sites at your checkups, at least once a year [11].

Gather the information and discuss it with your doctor. A pattern means at least 2–3 similar days, at the same time of day, with no obvious temporary cause. Write down the time, the value, the meal before it and your physical activity that day [14].

Patterns almost always have a simple solution, in this case probably a small reduction of the dose that acts in that time window [15]. The change is made in a single step and followed for a few days. Changing several doses at once makes it impossible to understand the result.

The doctor who follows you, together with you. Your doctor sets the doses, the treatment regimen and the adjustment rules you can apply on your own between checkups [11]. It is best if these rules are written down, personalized and tied to clear situations.

There is one universal exception, the time when your blood glucose is falling. In that case you take fast-acting carbohydrates right away [14]. A permanent change to a dose, however, remains a medical decision, because a change you make on your own can fix one hour and spoil the rest of the day.

This decision is made together with your doctor. The order of magnitude often used in practice is a small reduction, about 10–20% of the dose involved. Only one insulin dose is changed, usually the one that matches the time of the episode. After any adjustment, follow the effect for a few days, then discuss the result with your doctor so that the next step is as accurate as possible.

For a mild, isolated episode, its cause matters first [11]. If the cause is clear, such as unusual physical activity, there is usually no need to change the dose. A repeated pattern, however, calls for a careful review. A single level 2 or 3 episode is enough to reevaluate the treatment plan [14].