What is active insulin time?

What is active insulin and why is it so important to diabetes management? We asked Princess Margaret Hospital acting clinical nurse consultant/diabetes educator Liz Broad to explain the concept:

In the main, it is a safety feature used in pump therapy — and extended for use with bolus calculator meters — to help prevent over correction of elevated blood glucose levels (BGL) by giving insulin doses too close together.

Active insulin time refers to the time insulin remains working in your body and is usually set at three hours. This means that the impact lasts up to three hours after your injection or bolus of rapid acting insulin. Having elevated blood glucose levels immediately after meals doesn’t necessarily mean you need more insulin, but the insulin may still be working to bring the BGL down. So before you take more, you need to know how much active insulin you have. If the Bolus Wizard calculator recommends that you give a reduced amount of correction insulin or no correction insulin, it’s because you have insulin active in your system from a previous bolus. If, however, your BGL is still elevated after three hours, you will need more insulin to bring the BGL into target.

Knowing how much active insulin there is will help you to get an accurate dose of insulin to maintain proper blood glucose levels. If you give yourself an insulin injection too soon after a previous dose, your body will have too much insulin leading to low blood glucose levels. This is called insulin stacking — having another dose of insulin while the previous dose is still active — which can lead to hypoglyacemia.

For example: If you entered into your pump a blood glucose of 10.5mmol with 30g of carbs with background settings of a 1:10 carb ratio, a  BG target of 5.5mmol, and an insulin sensitivity of 2.5mmol, how much insulin do you estimate your pump would deliver? If you said 5 units of insulin, you’d be right unless you still have 2 units of insulin in your body from a previous bolus. Then you only need 3 units. Those 2 units from your last bolus is the active insulin.

Active insulin not only allows for more accurate dosing, it helps prevent insulin stacking. For more information, contact your clinic team.