What Is a Sensor-Augmented Insulin Pump (SAP)?

Girl wearing insulin pump and sensor device.

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Sensor-augmented insulin pumps (SAPs) are insulin pumps capable of talking to continuous glucose monitoring systems (CGMs). As an "open-loop" system, SAPs still require manual adjustments and inputs from the wearer. They are an important step toward the ultimate goal of a "closed-loop" system, which would work as an artificial pancreas capable of making insulin dose decisions on your behalf.

Insulin Pumps and CGMs

To prevent serious, life-threatening complications, people with type 1 diabetes must take insulin via injection at regular intervals throughout the day. Insulin pumps eliminate the need for multiple daily injections by pumping a slow and steady supply of insulin through a small catheter under the skin.

People with diabetes used to have to test their blood sugar levels on glucometers, which meant pricking their fingers with a lancet device several times per day. This added up to a lot of painful finger sticks.

Continuous blood glucose monitors (CGMs) like the Dexcom and Freestyle Libre have become very popular in the diabetes community because they reduce the need for finger sticks.

Fewer Needle Sticks

Insulin pumps cut down on the need for repeated injections, while CGMs cut down on the need for painful finger sticks.

CGMs use a small sensor under the skin that measures your glucose levels every few minutes and sends that data to your smartphone. This data can be uploaded to the cloud, where you and your healthcare provider can use it to look for patterns in blood sugar swings.

Many people use CGMs in conjunction with multiple daily injections, but the current gold standard in type 1 diabetes care involves using a CGM and an insulin pump.

How SAPs Work

Like standard insulin pumps, SAPs deliver insulin through a tiny cannula inserted just under your skin, usually on your abdomen, hip, or upper arm. Most pumps feature plastic tubing that connects to an insulin reservoir clipped onto your clothing. Tubeless insulin pumps, like the Omnipod, feature an insulin reservoir in a small pod that sticks to your body with adhesive.

All insulin pumps provide a continuous flow of short-acting insulin, known as a basal rate. With a standard pump, these rates are fixed and oblivious to real-time changes in blood sugar levels.

Sensor-augmented pumps allow your CGM to "talk to" your pump, so it can make adjustments to your basal rate based on real-time glucose data. This means your pump can automatically suspend your basal rate when your blood sugar levels are dropping. This reduces the risk of severe hypoglycemic episodes.

SAPs lower your risk of going too low by reducing or suspending your basal rate when your blood sugar is trending downward.

Closing the Loop

SAPs are a stepping stone toward a closed-loop insulin delivery system, which means that the pump acts as an artificial pancreas—reading glucose levels and dispensing the exact dose of insulin your body needs.

Closed-loop systems rely on complex algorithms able to predict what your blood sugar will be a half-hour in the future, based on your current blood glucose reading, how much insulin you've already taken, and other important factors.

Newer SAPs, including Minimed 770G and 630G and the Tandem t:slim X2, are known as hybrid closed-loop systems. These systems are not completely closed-loop because they still require input from the user. They can automatically adjust your basal rate when your blood sugar levels are outside of your target range, but you still have to tell the pump how many carbohydrates you eat at every meal and approve meal-time boluses.

Further, the algorithm doesn't know when you exercise or get sick, so it doesn't incorporate these factors into its predictions.

Pump Features

SAPs offer a variety of features to help improve your glycemic control, reduce your A1C, and prevent lows. As with standard pumps, when you first start an SAP, you will want to work closely with your healthcare provider or diabetes educator. Together, you can look at your blood sugar history to help you determine optimal insulin doses and other settings.

While some people use a single basal rate 24 hours a day, most people set different rates to begin at different times. For example, if your blood sugar tends to get low overnight, you may set your pump to give you a lower basal rate from 10 p.m. to 7 a.m.

Other critically important settings include your:

  • Insulin sensitivity factor (ISF): how far your blood glucose level drops when you take one unit of insulin
  • Insulin to carb ratio: how many grams of carbohydrates are offset by one unit of insulin

With an SAP, your pump settings are extremely important. Talk to your healthcare provider about your insulin sensitivity factor and your insulin to carb ratio.

Correction Boluses and Temporary Basals

Most currently available systems work in one of two ways to keep your blood sugar levels from exceeding your target range. The first is with a temporary basal increase. When your CGM detects a high blood sugar level, your pump automatically switches to a higher basal rate until the number comes back into range. While this is very effective, it can take a while to come down from a very high blood sugar level.

The second method is through an automatic bolus. When your CGM detects a high blood sugar level, your pump uses your settings to automatically give you a bolus. This way works more quickly on high blood sugars than the first, but may increase the risk of hypoglycemia.

Most hybrid closed-loop systems also have the option for you to manually increase or decrease the basal rate temporarily. For instance, you may want to reduce your basal rate by 50% when you are exercising.

Bolus Calculator

SAPs are also capable of delivering a larger amount of insulin before meals. Your personal insulin to carb ratio should be customized and set by your healthcare provider. Based on your settings and your current blood sugar level, SAPs will recommend a bolus amount. All you have to do is make sure you accurately count how many carbohydrates you plan to eat. You enter the carb amount into your pump and then choose whether to accept and deliver the recommended bolus.

Automated Insulin Suspension

This feature allows insulin delivery to be suspended automatically when the continuous glucose monitor detects that the glucose level has fallen and there is a risk of hypoglycemia.

A 2013 study in Australia of 95 patients with type 1 diabetes concluded that this reduced the rate of severe and moderate hypoglycemic episodes compared with standard insulin pump therapy.

Side Effects

As with all forms of insulin therapy, SAPs come with the risk of hypoglycemia. Accidentally using too much insulin will remove glucose too quickly from the bloodstream, causing symptoms like dizziness, confusion, shakiness, sweating, seizure, and loss of consciousness.

Fortunately, there is evidence suggesting that SAPs cause fewer episodes of hypoglycemia than multiple daily injections. While research into SAPs is ongoing, previous research has shown that CGMs can reduce both the frequency and severity of hypoglycemic events.

Cost

On average, an insulin pump costs around $6,000 and annual supplies may range from an additional $3,000 to $6,000. Most insurance companies will pay for insulin pump therapy, but coverage of out-of-pocket expenses may vary. Contact your insurance company to find out what your particular plan covers. Many companies require a prior authorization form from your healthcare provider before they will approve coverage.

Questions for Your Healthcare Provider

If you are interested in trying an SAP, make an appointment with your healthcare provider and talk to them about whether this type of insulin therapy is right for you. Here are a few questions to consider asking:

  • Will this device help me better manage my glucose levels?
  • What are the possible side effects of using this device?
  • What should I do if my diabetes medications cause my blood sugar to drop too low?
  • What should I do if I'm sick or if I exercise?
  • Should I take a bolus of insulin before or after meals and snacks?
  • If I travel, how can I continue to effectively manage my condition?
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4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Ly TT, Nicholas JA, Retterath A, Lim EM, Davis EA, Jones TW. Effect of sensor-augmented insulin pump therapy and automated insulin suspension vs standard insulin pump therapy on hypoglycemia in patients with type 1 diabetes: A randomized clinical trial. JAMA. 2013;310(12):1240-7. doi:10.1001/jama.2013.277818

  3. Allen N, Gupta A. Current diabetes technology: Striving for the artificial pancreas. Diagnostics (Basel). 2019;9(1):31. doi:10.3390/diagnostics9010031

  4. McAdams BH, Rizvi AA. An overview of insulin pumps and glucose sensors for the generalist. J Clin Med. 2016;5(1). doi: 10.3390/jcm5010005

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