Pump Terms

Glossary letters

  1. 4 terms starting with A
  2. 6 terms starting with B
  3. 9 terms starting with C
  4. 6 terms starting with D
  5. 1 terms starting with E
  6. 2 terms starting with F
  7. 2 terms starting with G
  8. 4 terms starting with H
  9. 6 terms starting with I
  10. No terms starting with J
  11. No terms starting with K
  12. 2 terms starting with L
  13. 3 terms starting with M
  14. 2 terms starting with N
  15. 1 terms starting with O
  16. 6 terms starting with P
  17. No terms starting with Q
  18. 1 terms starting with R
  19. 6 terms starting with S
  20. 7 terms starting with T
  21. 1 terms starting with U
  22. No terms starting with V
  23. No terms starting with W
  24. No terms starting with X
  25. No terms starting with Y
  26. No terms starting with Z

Reference

  1. 01A to Z glossary

Explainers

  1. 02How an insulin pump works
  2. 03Pump or injections?
  3. 04Infusion sets and site rotation
  4. 05Carbohydrate counting
  5. 06Alarms and fail-safes
  6. 07Sick days
  7. 08Exercise
  8. 09School and nursery
  9. 10Travelling with a pump

Related reading

  1. 11Diabetes and the nervous system
  2. 12Official UK guidance

About

  1. 13About
  2. 14How we check facts
  3. 15Contact
  4. 16Privacy

How an insulin pump works

A plain-language outline of continuous subcutaneous insulin infusion, the parts of a pump, what it does and does not do, and who looks after it in the UK.

Updated 11 October 20265 min readGeneral information, not medical adviceBy the Pump Terms editors

Schematic of a tubed insulin pump system A pump body with a cartridge connects by a thin tube to an infusion set stuck to the skin. A small flexible tube, the cannula, passes through the skin into the fatty layer beneath. 1 2 3 4 5
Schematic of a tubed pump system, not to scale.
  1. Pump body: the unit with the screen and controls
  2. Cartridge: the reservoir that holds the insulin
  3. Tubing: carries insulin from the pump to the set
  4. Infusion set: the adhesive pad stuck to the skin
  5. Cannula: the soft tube that sits just under the skin

An insulin pump is a small, wearable device that delivers insulin through a thin tube placed just under the skin. NHS information describes it as a device you attach to your skin and wear all the time, giving tiny amounts of insulin throughout the day and night. This page is a general outline, not personal advice, and decisions about any individual's treatment belong with their own diabetes team.

What CSII means

The clinical name for pump therapy is continuous subcutaneous insulin infusion, usually shortened to CSII. "Subcutaneous" means under the skin, and "infusion" means a steady delivery over time. NICE's guideline on children and young people with diabetes defines an insulin pump as a programmable pump and insulin storage device that gives a regular or continuous amount of insulin, usually a rapid-acting insulin analogue or short-acting insulin, through a subcutaneous needle or cannula. You can find the shorter terms in the glossary entry for pump therapy and the entry for subcutaneous.

Diabetes UK adds that you only need one type of insulin in the pump, known as fast-acting insulin. Because a pump holds no long-acting insulin, people are advised to keep a back-up kit for injections in case the pump stops working.

The parts of a pump system

A pump system has a few pieces, and the names vary between manufacturers. The general layout is the same.

  • The pump itself, which holds the controls and the mechanism that pushes insulin out.
  • A cartridge (also called a reservoir), which holds the insulin. Diabetes UK uses the word "reservoir" for the insulin store in the pump.
  • An infusion set, which carries insulin from the pump to the body.
  • A cannula, the tiny tube that sits just under the skin and is part of the set.

Diabetes UK describes two broad designs. A tubed (tethered) pump connects to the cannula through a length of tubing, and can be carried on a belt, in a pocket or in a body band. A tubeless patch pump sits directly on the skin where the cannula is placed and is controlled with a handheld device. Diabetes UK also notes that a patch pump is disposable, so the whole device is changed when the pump alerts you, rather than just the set. How often parts are changed, and where they go on the body, is covered on the page about infusion sets, cannulas and site rotation.

Basal and bolus delivery

A pump delivers insulin in two ways. A programmed background supply of small amounts, set in blocks of time, does the job of basal insulin. Diabetes UK says the healthcare team can help set these rates, and that they can change depending on things like how active a person is.

The second kind of delivery is a bolus, an extra amount given for food or to bring down a high reading. According to Diabetes UK, most pumps have a bolus calculator: the person enters the carbohydrate they plan to eat and their current glucose reading, and the pump does the arithmetic, taking active insulin into account. The settings behind that calculator are set up with the team and differ from person to person, so this page gives no values. The way the counting works is explained under carbohydrate counting and boluses.

What a pump does not do by itself

A pump on its own does not measure glucose. It delivers the insulin it has been told to deliver. Glucose still has to be checked, either with finger-prick tests or with a sensor, and the person (or their carer) has to give boluses for meals unless the system is one of the linked types described below. Diabetes UK also lists some practical downsides: the pump needs to be attached most of the time, and the infusion set can become blocked or detached, which could lead to high glucose and raise the risk of diabetic ketoacidosis. Because the pump holds only fast-acting insulin, a delivery problem can matter quickly.

The Chelsea and Westminster NHS leaflet on troubleshooting makes the same point from the clinic side: if a pump stops working, a back-up plan is essential, because only quick-acting insulin is in the pump. Alarms and what they mean are covered on the page about alarms, occlusions and fail-safes.

Linking a pump to a sensor

Some pumps can talk to a continuous glucose monitor (CGM), a sensor worn on the body that reads glucose at intervals. The NHS says that when a pump works with a CGM, it can automatically give the right amount of insulin based on glucose levels, and calls this a hybrid closed loop system. NICE, in its appraisal TA943, explains that these systems deliver insulin automatically using a calculation based on continuous glucose measurements, but that manual insulin dosing is still needed sometimes, for example around mealtimes. "Hybrid" refers to that shared job between device and person. Diabetes UK points out that for a hybrid closed loop you need a pump that can be connected to a CGM. The wider idea is sometimes called automated insulin delivery.

The NHS describes these systems as gradually being made available. NICE's recommendations for who can have one are summarised on the page pump or injections, and what NICE says.

Who looks after pump therapy

Pump therapy is run by a specialist diabetes team rather than by the device alone. NICE's technology appraisal TA151 recommends that CSII be started only by a trained specialist team, which should normally include a physician with a specialist interest in insulin pump therapy, a diabetes specialist nurse and a dietitian. Diabetes UK says pump training and ongoing support should come from the diabetes healthcare team, and that manufacturers also give technical support and have helplines. For children and young people, NICE's guideline says a specialist team should provide ongoing support, so the paediatric diabetes team usually takes that role.

Anyone with a safety concern about a pump can report it through the Yellow Card scheme, according to Diabetes UK. Teams differ, so the team's own advice has the final word.

Questions people ask

Does a pump replace injections completely?

It replaces the routine of regular injections, but not the need for a way to inject. Diabetes UK says to keep a back-up kit, because insulin has to be given another way if the pump fails.

Is a pump the same as a sensor?

No. A pump delivers insulin, while a sensor measures glucose. They can be linked in some systems, but they are separate devices that do different jobs.

Can a pump be used with other types of diabetes?

Diabetes UK says pumps are generally licensed and recommended for children and adults with type 1 diabetes, and that people with other types may also be able to benefit. NHS provision is generally limited to some people with type 1 diabetes.

In short

An insulin pump gives a steady background supply of fast-acting insulin through a cannula under the skin, plus extra boluses for food or high readings. It does not measure glucose unless it is linked to a sensor, and even a hybrid closed loop still needs some input from the person. A specialist diabetes team trains, supports and reviews anyone who uses one.