In the pump we use only rapid-acting insulin

Written by Assoc. Prof. Dr. Sorin Ioacara Sources verified Updated: September 7, 2026 7 min read

A pump takes a single kind of insulin, the rapid-acting one, used in two ways: a small and almost continuous flow for the basal need and larger doses at meals.

only rapid-acting insulin
the only type of insulin suitable for a pump
every 3 days
you change the insulin together with the reservoir and the infusion set
U-100
the standard concentration, 100 units per milliliter

What kind of insulin is used in a pump?

In an insulin pump only rapid-acting insulin is used. This is the only suitable type, because the pump delivers small amounts under the skin at short intervals (on many pumps, every five minutes), and rapid-acting insulin has a prompt and predictable effect [1].

Rapid-acting insulin starts working quickly and is used up in a short time. The pump can therefore adjust insulin delivery rapidly and can cover both the background part between meals and the rises in blood glucose at the meal, as the figure below shows [2].

Figure 1

What insulin goes into a pump

  1. The only suitable oneRapid-acting insulinIts effect is prompt and predictable, exactly what the pump needs.
  2. How the pump worksSmall amounts, at short intervalsIn general, once every five minutes.
  3. A single typeIt covers both the background and the mealsThe same insulin covers the background part between meals and the rises in blood glucose at the meal.
  4. NeverLong-acting insulinIts absorption stretches over many hours, so it would make delivery hard to predict.
Only rapid-acting insulin goes into a pump [1]. It starts working quickly and is used up in a short time, which lets the pump adjust as it goes [2]. Long-acting insulin is never put into a pump, because its long absorption would take away the very rapid control the pump gives you [3].

Can I use long-acting insulin in a pump?

No, long-acting insulin is never put into a pump. It is designed to be absorbed slowly, over very many hours, and it does not fit the way the pump works [3].

The pump creates the effect of basal insulin on its own, through small amounts of rapid-acting insulin delivered at short intervals, on many pumps once every five minutes [1]. If you were to put in long-acting insulin, delivery would become hard to predict and you would lose the rapid control that the pump gives you.

Does a single type of insulin cover both the basal need and meals?

Yes. The same rapid-acting insulin covers both needs. Delivered in an almost continuous flow, it provides the foundation needed between meals and overnight, that is, the basal need.

The same insulin, delivered in a larger amount when needed, covers the meal or corrects a high blood glucose. A single rapid-acting insulin used in two different ways is the basic principle of the pump [1].

How often do I have to change the insulin in the pump?

As a rule you change the insulin in the pump every three days, together with the reservoir and the infusion set. The insulin left in the reservoir, at body temperature, gradually loses its potency and it is not good to reuse it [4].

Put in fresh insulin every time, without topping up over the old one. Follow the manufacturer's instructions, because some situations call for an earlier change. If needed, change the infusion set together with the reservoir and the insulin even if you fitted it only a few hours ago. Changing it in time when required reduces the risk of high blood glucose that cannot be corrected [5].

How should I store insulin before putting it in the pump?

Spare insulin, still unopened, is kept in the fridge, at about 2–8°C. Never freeze it, and if it has frozen, do not use it anymore [6] [7].

Let the insulin reach room temperature before you fill the reservoir, so that you avoid the formation of air bubbles, which can partly interrupt delivery. Keep it away from sources of heat and from direct sunlight.

Can heat damage the insulin in the pump?

Yes, heat is insulin's main enemy. Heat sources such as strong sun, a hot car, the sauna or hot water can degrade the insulin in the pump and gradually reduce its effectiveness (potency) [7] [8].

The main sign that warns you is a high blood glucose that you cannot explain, even though the doses seem correct [9]. Wear the pump shielded from the sun. In a heatwave, do not leave it pressed right against your skin under thick clothes. Replace the insulin if it has been in excessive heat.

What happens if I run out of insulin in the pump?

The pump uses only rapid-acting insulin and does not leave a long-acting reserve in the body. That is why, 1–2 hours after delivery stops, blood glucose starts to rise, and at some point ketone bodies build up and the risk of ketoacidosis appears [10]. So you check for ketone bodies in the blood as soon as delivery stops, or if blood glucose stays high after a correction. Between 1.5 and 2.9 mmol/L, contact your medical team immediately. At 3.0 mmol/L or above, or if vomiting, difficulty breathing or drowsiness appear, go to the emergency room straight away.

If the alarms are switched on, the pump warns you with a sound or a vibration when the reservoir is empty or when a blockage occurs, so react immediately. Always keep spare insulin at hand. Check your blood glucose and ketone bodies (with a dedicated sensor, a meter or urine tests) [1].

Does the concentration of the insulin used in the pump matter?

Yes, it matters a great deal. Every pump is set for a certain insulin concentration, most often that of 100 units per milliliter, called U-100. The pump measures a volume of liquid and turns it into units on the basis of this concentration [11].

If you put in an insulin whose concentration does not match the one the pump is built for, the actual dose would be wrong, too large or too small. Use only the concentration approved for your pump and never mix different concentrations [12].

Conclusions

  • In a pump you put only rapid-acting insulin, because its effect starts promptly and ends predictably [1] [2].
  • Long-acting insulin is never put into a pump, and the same rapid-acting insulin covers both the basal need and meals [3].
  • The insulin in the reservoir sits at body temperature, which is why it is changed about every three days, together with the reservoir and the infusion set [4] [5].
  • Spare insulin is kept at 2–8°C and never frozen, and sustained heat gradually reduces its potency [6] [7] [8].
  • If delivery stops, blood glucose starts to rise within 1–2 hours, so you check for ketone bodies in the blood and always keep spare insulin at hand [10].
  • Use only the concentration approved for your pump, most often U-100, that is, 100 units per milliliter [11] [12].

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Glossary terms used here

References

  1. American Diabetes Association Professional Practice Committee. 7. Diabetes Technology: Standards of Care in Diabetes-2026. Diabetes Care. 2026;49(Suppl 1):S150-S165. PubMed
  2. Bramlage P, Tittel SR, Müther S, Reinhart-Steininger B, Haberland H, et al. A comparison of the rapid-acting insulin analogue glulisine with lispro and aspart for the pump treatment of patients with type 1 diabetes. Acta Diabetol. 2022;59(11):1453-1460. PubMed
  3. American Diabetes Association Professional Practice Committee. 9. Pharmacologic Approaches to Glycemic Treatment: Standards of Care in Diabetes-2026. Diabetes Care. 2026;49(Suppl 1):S183-S215. PubMed
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