Insulin delivery methods

If you have type 1 diabetes you will be taking insulin either via multiple daily injections (often referred to as a basal-bolus regime or MDI), or via a continuous subcutaneous insulin infusion (CSII), also called an insulin pump.

On MDI you would take around three injections per day of rapid-acting insulin before main meals and one or two injections of long-acting insulin that will work in the background. The rapid-acting insulin injections are called bolus doses or boluses. This insulin is there to minimise any glucose spikes after a meal. The background insulin is referred to as your basal insulin and is meant to keep your glucose levels steady across the day and night.

An insulin pump is a computerised, programmable device that has a cartridge filled with rapid-acting insulin in it. This rapid-acting insulin works both as a basal insulin, by delivering the insulin little by little, drop by drop in the background, based on certain settings, and as your bolus doses based on your personal profile and carbohydrates you enter into a ‘bolus calculating wizard’.

The pump is worn day and night and would only be disconnected when you have a shower, bath, go swimming or if you play contact sports.

Insulin bolus calculations

People with diabetes who are on a basal-bolus insulin regimen, (this can also include people with type 2 diabetes), need to calculate their rapid-acting insulin multiple times per day, before each main meal.

This is a challenging and demanding task that can leave a lot of room for error as you will need to consider lots of different factors. These include:

• Your current blood glucose level and glucose trends
• Your food intake
• Any exercise, both planned and incidental
• Any insulin left on board from previous injections
• Your insulin action time

Calculating bolus insulin injections accurately will help optimise Time in Range (TIR) whilst reducing your risk of hypoglycaemia, or low blood glucose levels. Miscalculating rapid-acting insulin doses can lead to either hypo- or hyperglycaemia (high blood glucose levels) and can increase your risk of developing diabetes-related complications in the long-term.

If you are on multiple daily injections you can use your phone as an insulin bolus calculator.

Insulin bolus calculators

Bolus calculators have been available as stand-alone devices or integrated in insulin pumps for quite some time. Now they are also available in the form of software applications that can be downloaded onto smart devices.

Bolus calculator mobile phone apps can result in substantial improvements in HbA1c and TIR as they can help you calculate how much rapid-acting insulin you need to take before a meal based on some pre-set and personalised parameters.

The pre-set parameters generally include:

• A Blood Glucose Target which will allow the calculator to correct high or low blood glucose levels to this pre-set value or glucose range. High glucose levels will result in additional insulin being recommended, whereas a low glucose level will result in a reduction in the suggested dose.
• The Insulin Sensitivity Factor (ISF), which is sometimes also referred to as the Correction Factor, is the measure of how much one additional unit of rapid-acting insulin is expected to drop your glucose level by.
• The Insulin to Carbohydrate Ratio (ICR) tells you how many grams of carbohydrates are covered by one unit of rapid-acting insulin.
• Any Insulin left On Board (IOB) can be included in the calculation by deducting the IOB from the correction bolus. This will help reduce the risk of hypoglycaemia.
• The Duration of Insulin Action (DIA) is used in the IOB calculation. It describes how long injected rapid-acting insulin remains active in your body. The DIA is generally anywhere from three to five hours.

Bolus calculator apps

Bolus calculators should be considered ‘medical devices’. In Australia the Therapeutic Goods Administration (TGA) regulates guidelines for medical devices. However, most diabetes app manufacturers make claims that are currently not backed by appropriate scientific evidence.

Apps can range in functionality from being simply a reminder system, to providing modest information, social networking or clinical statistics, all the way through to the more complex analysis of glucose patterns to analyse insulin dose recommendations and blood glucose predictions. Some apps allow for data sharing with health care professionals.

Some commonly recommended (and currently TGA approved) apps for insulin dose calculations in Australia are:

• Accu-Chek^® Connect app by Roche Diabetes Care Australia
• The mylife^TM App by Ypsomed Australia
• The mySugr Bolus Calculator App by Roche Diabetes Care Australia

All three of these apps are available on Google Play and in the App Store.

Get advice

As always, we recommend that you talk to your diabetes health professional about which app they recommend you use, in your unique situation. Your diabetes health professional can help you set up your personalised parameters in the app.

Carolien Koreneff, CDE-RN, FADEA