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Getting the most out of injections and insertions

Deciding on an insulin dose means juggling multiple factors; testing your current blood glucose level, counting the carbohydrates in your meal, estimating glycaemic index and considering any physical activity you might do in the next few hours. But the thinking isn’t over when you go to inject or bolus – let’s discuss five important things to remember when you dose your insulin that will maximise its effectiveness.

Needle needs Pens: The skin is about 2mm thick and insulin needs to be injected into the layer of fat just below the skin. Pen needles for injecting insulin come in lengths from 4mm up to 12.7mm. Recent studies evaluating insulin dose effectiveness for different needle lengths have found that short needles (4-6mm) are safe and effective, regardless of age or body size - in fact, a 4mm pen needle is estimated to deliver insulin into the fat layer more than 99.5% of the time. Pumps: There are over 20 different insulin pump infusion sets available, with varying compatibility with different brands of pumps. Each pump type has both plastic and steel cannula options; steel cannulas are generally preferred by people who react to plastic or who have had problems with plastic cannulas bending. Cannula lengths and recommended insertion angles vary, according to factors like level of activity, site placement, and leanness/muscularity. Most people can use a plastic 6mm cannula that inserts at 90° without issues. If you have scar tissue or are noticing some unexplained insulin resistance, you might need to try a 9mm. A 13mm or 17mm cannula with an insertion angle of 30-45° can be used by people who are lean or muscular and women in the later stages of pregnancy when the skin is stretched.  Life-changing Pens: Change your needle before every injection. Re-used needles can become distorted and blunt, increasing pain at the injection site. Blunt needles cause damage, leading to toughened skin, unsightly marks and infection risk. Pumps: Change your site every three days in order to maintain optimal insulin absorption and avoid infection. Avoid changing insulin pump infusion set sites at bedtime, as an unsuccessful insertion could lead to high blood glucose levels, which may not be picked up and corrected until morning. Rotation reiteration It’s vital to rotate injection and pump sites regularly. Rotating sites gives each area time to heal and prevents lipohypertrophy - lumps under the skin caused by the accumulation of extra fat at the site of many injections of insulin. Lipohypertrophy may be unsightly, mildly painful, and can affect insulin absorption. Avoid injecting or placing an infusion site close to your continuous glucose monitor site to prevent overuse in a particular area. Areas of scar tissue, moles or skin with unusual texture may impact insulin absorption so it is best to avoid these altogether.  Injection directions If you’re on injections, correct injection technique will minimise insulin leakage. Follow these tips:

  • Prime! This removes any air from the needle and ensures the pen is working. Dial-up 2 units and shoot them into the air, making sure you see the drops of insulin on the end of your needle.

  • Inject at a 90° angle to the skin. You might need a 45° angle if you’re very lean.

  • Pinching the skin to inject is generally not needed, even for 4mm needles. It might be warranted in very lean people or in young children.

  • Hold the needle in place for 10 seconds after injecting to prevent insulin leakage

  • Injecting large doses into one site can affect absorption. Try splitting your larger doses over two injection sites and monitor to see if they’re more effective.

Absorb this Insulin absorption rates are individual. You can assess how quickly insulin absorbs from an injection site by monitoring the rate at which your blood glucose levels change after you inject - continuous glucose monitor arrows are a great tool here (although remember, there is a 10-minute time lag between CGM readings and blood glucose). In general, insulin is absorbed fastest from the stomach, followed by the arms, thighs and buttocks. Be aware that the absorption rate can be impacted by factors such as heat and blood flow. Injecting over a working muscle, moving/exercising the limb that had the injection, rubbing or warming the injection site after you inject (including getting into a warm shower or bath), or accidentally hitting muscle instead of injecting into fat - a risk if you're using a long needle - can all increase the speed at which insulin acts and may lead to unpredictable blood glucose levels and hypoglycaemia. If want to make sure your injection or insertion technique is on point, ask your diabetes educator to watch you inject or insert your infusion set and give you advice. They can also help you assess your sites for any signs of lipohypertrophy or other factors that may impact the effectiveness of your insulin. Making minor changes to your technique can have big benefits: it can improve the effectiveness of your insulin doses and lead to more time spent in your target zone! Images courtesy of and Diabetes Forecast

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