Does your blood sugar level seem unpredictable at times? If you live with insulin-dependent diabetes, it is probably so and sometimes it can be difficult to determine what is going on.
If you’re not paying attention to IOB, your blood sugar levels look random and unpredictable, so it’s important to learn how to calculate insulin on the board (IOB)
Paying attention to IOBs doesn’t solve all the daily blood sugar calamities, but they are extremely helpful. This is a key component for better diabetes management, something that is not raised frequently or fully taught when diagnosed.
Knowing IOBs can help you to make a good decision, such as whether your blood sugar levels are no longer low and it’s safe to go for a walk, if you need to inject insulin to correct your high blood sugar, or if you don’t need to wake up in the middle of the night to treat your hypoglycemia, or if you need to inject more insulin.
What is insulin on board?
The insulin you board is how active and rapidly acted insulin in the body. We’ve also seen it called Bob (inboard bolus), or unused insulin.
Rapidly acting insulin is the type of insulin people with insulin-dependent diabetes that we use when we need to correct or correct highs. Common brand names for active insulin are Humanlog, Novolog, and Fiasp. It is also the type of insulin used in insulin pumps.
Too much IOB will cause low blood sugar levels (hypoglycemia) and too little for hyperglycemia (hyperglycemia).
IOB is important as the injected, rapid-acting insulin can last 3-5 hours in the body. This means that you need to pay attention not only to the number of insulin units to be injected with, but also to the remaining dose up to 5 hours after injection.
Since we all metabolize insulin at slightly different rates, how long does it range in the body (3-5 hours). Most insulin pumps are set at 3 hours, and most doctors recommend checking the IOB after about 2 hours of the dietary bolus to see if sufficient dietary bolus has been administered.
If you use an insulin pump, the pump will tell you the IOB from all the bolus.
However, it is worth noting that insulin also does not contain a rapidly acting basal (background insulin). Exercise is especially problematic when discussing active insulin overlooking the basal insulin of the pump. This is because too many IOBs from the bolus or pump base will lower your blood sugar levels.
If you are using an insulin pen, there are several apps that can help you calculate and track your IOBs, such as RapidCalc (not FDA approved) and MySugr (EU only). There is also a smartpen called inpen available in the US
How to calculate IOB
If you don’t have access to the device or app that calculates your IOB, or if you want to know about “Pump Basal IOB”, you can calculate your IOB fairly easily.
This video shows an example of how to calculate the “pump base IOB” and IOB from injection.
It is recommended to do exercises that calculate your IOB several times and start paying attention to how different levels of IOB affect your blood sugar levels in different situations.
Here are two additional examples:
Example of base IOB (pump)
Assuming that insulin is active in the body for 4 hours, the basal per hour is 1 IU.
1 IU X 25% + 1 IU X 50% + 1 IU X 75% + 1 IU X 100% = Total: 2.5 IOB
Examples of Bolus IOB (MDI)
Assuming that 1 IU is injected 1 hour before, 2 IU is injected 3 hours before, and insulin is active in the body for 4 hours:
2 IU x% + 1 IU x 75%= 1.25
Why should you be concerned about IOB?
Knowing the IOB can be an important factor in understanding whether you have the right amount of insulin for a particular activity. This is the only best indicator of how blood sugar levels respond during different times and activities.
One of the first things many people have been taught after being diagnosed with diabetes is that they have a bad build-up of insulin. Stacking insulin means taking one or more rapid action insulin during a 3-5 hour time frame while active in the body.
However, if you don’t get enough insulin at the first dose, just wait 3-5 hours while your blood sugar levels are high before correcting. Your IOB will help you decide that.
When calculating the insulin dose, the IOB must be a component of the calculation. Here’s the calculation:
Carbohydrate insulin you eat +/- correction for your current blood glucose – IOB = dose recommendation
So I’m not eating, my blood sugar level is 250 mg/dL, my target blood sugar level is 100 mg/dL, my correction factor is 50, and IOB is 1 IU. This is a calculation.
0 IU + 3 IU corrected dose ((250-100)/50))) for carbohydrates – 1 IOB = 2 IU
If I hadn’t considered the IOB, I would have just injected 3 IU and probably would have been low.
Another important factor is reducing the risk of hypoglycemia. The only reason we get low is that if your system has too much insulin, then there are too many IOBs. So paying attention to the IOB needs of various activities is key to knowing whether it’s suitable for what we’re trying to do, or whether we need a small carb snack first.
When is it important to pay attention to the IOB?
It is important to focus on the IOB throughout the day, but these are the three most important times to pay particular attention to.
When exercising
Your insulin sensitivity increases during and after exercise, increasing the risk of hypoglycemia. By paying attention to IOBs, you can adjust your IOBs to allow you to exercise with a balanced blood glucose level (by adjusting insulin before exercise) depending on how your blood glucose levels respond when you do different types of exercise.
And in situations where you can’t plan ahead, you’ll know if you have too many IOBs and need carb snacks.
Before going to bed
Good night sleep can be difficult with diabetes, and no one wants to deal with hypoglycemia at night or wake up with a blood glucose hangover after eating high blood glucose all night.
Checking your IOB and blood glucose levels before bed can help you assess whether you need a snack to prevent hypoglycemia, or whether you need to take a corrective dose due to hyperglycemia.
Before eating or editing
The IOB should be part of all diet and correction calculations, allowing for more accurate insulin doses.
Knowing the IOB allows you to take the doses as needed and eat when you feel like it, which will help you build confidence in the insulin dose you take.
