Beta cells in the pancreas produce insulin and release it into the bloodstream after people eat. Insulin enables body cells — such as muscle, fat, and heart cells — to absorb the sugar from food and use it for energy and other essential processes.
When a person eats, they do not immediately use all the energy they get from a meal. Insulin helps the body to store glucose in the liver as glycogen. The liver releases it when blood sugar levels are low, or when a person needs more energy.
Insulin is essential for regulating blood sugar, ensuring that levels remain within certain limits, and stopping them from rising too high or falling too low.
After scientists discovered how to use insulin to treat diabetes, it became possible for people with diabetes to live full and productive lives.
However, the person needs the right amount of additional insulin for the best effect. The amount can vary over time and between individuals.
The American Diabetes Association (ADA) note that careful blood glucose control may reduce the risk of complications for people with type 1 diabetes.
This article looks at ways of assessing how much additional insulin a person with type 1 diabetes needs in order to adjust their insulin dose to stay healthy. It also looks at ways of controlling blood glucose levels when a person has type 2 diabetes.
What is insulin sensitivity factor?
Knowing how to calculate the insulin sensitivity factor can help a person with diabetes to get the correct dose of insulin.
A person with diabetes needs to keep their blood sugar levels within a target range to stay healthy. Insulin can stop blood sugar levels from rising to dangerously high levels.
When a person takes insulin, their blood sugar levels fall. However, if blood sugar levels fall too far, this can be dangerous, too.
Insulin sensitivity factor, or correction factor, refers to the number of milligrams per deciliter (mg/dL) by which blood sugar levels fall when a person takes 1 unit of insulin.
A person with type 1 diabetes can use this number when deciding how much insulin they need to keep their blood sugar levels within the target range.
They will usually add this amount to their existing premeal insulin dose. The amount will depend on how much higher the person's blood sugar level is, compared with their target.
A person will work with their doctor to fix their personal target blood sugar levels.
According to the ADA, the target level should be as close as possible to the levels that a person without diabetes would have.
- Between 70–130 mg/dL before a meal
- No higher than 180 mg/dL up to 2 hours after a meal
Insulin treatment plans vary, but most people with type 1 diabetes now use two types of insulin:
- Basal insulin, a longer-acting form that keeps blood sugar levels stable between meals and when sleeping.
- Bolus insulin, a faster-acting form to regulate levels around mealtimes.
Some people use an insulin pump. The pump delivers an amount of fast-acting insulin throughout the day and night and another amount of insulin for mealtimes.
The 1800 rule and calculation
People who use this type of pump can use a calculation to find out how much rapid-acting insulin they need to reduce blood sugar by a certain amount.
The ADA give full instructions for deciding how much insulin a person needs when using an insulin pump. The individual should calculate this with the help of their healthcare provider.
- The person should identify how much insulin they need by finding the average amount they use over several days. The amount may depend on the type of insulin the person uses.
- They should then divide the total so that the basal insulin is 40–50 percent of the total amount and the bolus amount is 50–60 percent.
- Next, they will divide the total by 24 to find out how much basal insulin they need each hour.
- Next, they should adjust the hourly amount, depending on activity levels and food consumption during the day.
- After that, the person should use something called the "500 rule" to find out how many carbs 1 g of insulin will cover. This will tell them how much bolus insulin they need to cover the number of carbs they plan to eat.
- Finally, they will use the 1800 (or 1500) rule to find out how much insulin they need to correct high blood glucose. This rule works by dividing the number 1,800 by the total average daily dose of fast-acting insulin to see how much one unit of insulin will lower their blood sugar levels.
Finally, the person should discuss the results with their healthcare provider before making any changes, especially for a child or a person with a recent diagnosis.
Adjusting a dose incorrectly could be dangerous.
What is the 1800 rule?
For example, if a person is taking a total of 30 units of rapid-acting insulin through the day, they would calculate like this:
- They divide 30 into 1,800.
- This gives an insulin sensitivity factor of 60.
This means that 1 unit of fast-acting insulin would reduce this person's blood sugar levels by 60 mg/dl.
Imagine that a person's target goal is to have their glucose at 100 mg/dL before meals, but their actual glucose is 220 mg/dL before the meal. The person will calculate like this:
- 120/60 is 2
They will add 2 units of fast-acting insulin to their insulin amount for that meal.
For regular insulin, the person would divide into 1,500 instead of 1,800. However, most people do not use this type of insulin nowadays.
How to test for insulin sensitivity factor
People should check their insulin sensitivity factor and blood sugar levels regularly.
A person should test their insulin sensitivity factor every day.
To do this, they will:
- Check and record their blood sugar levels.
- Take a correction dose of insulin, based on their current sensitivity factor.
- Retest their blood sugar levels 2 and 3 hours after taking the insulin dose.
If the ratio is correct, the person's blood sugar level should be within a 40-point range of their target.
If it is out of this range on two or more occasions, they may need to change their correction factor. The person should speak to their doctor about this. They may need further testing to confirm the results.
If blood sugar levels drop below 70 mg/dL, the person should stop the assessment and treat their low blood sugar, for example, by eating or drinking something.
Blood glucose testing kits are available for purchase online.
Anyone who believes they need to adjust their insulin sensitivity factor should speak to a healthcare provider before taking any action.
When to test for insulin sensitivity factor
Many things can affect insulin sensitivity factor during the day, so it is important to choose the right time of day to test.
Doctors recommend assessing insulin sensitivity factor when:
- Glucose testing shows that blood sugar levels are at least 50 mg/dL above target.
- The person has not eaten for at least 4 hours.
- They will not eat for the next 4 hours.
- They have not taken a bolus insulin dose for at least 4 hours.
People should not test for insulin sensitivity factor:
- after strong physical activity
- during an illness or infection
- after a period of low blood sugar levels
- during times of emotional stress
How diabetes type 1 and 2 affect insulin
The two main types of diabetes affect insulin in different ways.
Type 1 diabetes
The body of a person with type 1 diabetes cannot produce the insulin the person needs to regulate their blood sugar levels.
Exactly why this happens is unclear, but it may be that the person's immune system mistakenly attacks and destroys the beta cells in the pancreas that produce insulin.
According to the ADA, around 5 percent of people with diabetes have type 1 diabetes. It can occur at any age, but it usually develops in childhood or young adulthood.
The symptoms of type 1 diabetes start to appear more quickly than other types of diabetes, as more and more insulin-producing beta cells stop working.
The symptoms include:
People with type 1 diabetes need to take insulin every day to control their blood sugar levels, because their body cannot produce insulin naturally.
They can inject insulin using a syringe or a continuous-release insulin pump. Insulin is essential for key body functions, so the person will need daily injections for life.
Type 2 diabetes
Diabetes can lead to a range of symptoms.
Type 2 diabetes is a metabolic condition in which the body either:
- cannot produce enough insulin
- cannot use the insulin it produces effectively
When the body cannot use the insulin it produces effectively, this is called insulin resistance.
According to the Centers for Disease Control and Prevention (CDC), around 90–95 percent of people with diabetes have type 2.
Risk factors for type 2 diabetes include:
- having excess weight
- being aged 45 years or over
- doing physical activity less than three times a week
- having a family member with type 2 diabetes
- having high blood pressure, high levels of triglyceride (fat) in the blood, or high overall cholesterol levels
Doctors advise people with type 2 diabetes to manage their blood sugar through:
- a healthful diet
- regular exercise
- weight control
- medications, if necessary, to keep glucose levels within target
If a person has a diagnosis in the early stages, there is a good chance that they can use these strategies to prevent type 2 diabetes from progressing or developing fully.
Find out more here about how dietary choices can stop prediabetes from becoming type 2 diabetes.
Both type 1 and type 2 diabetes can lead to a number of complications, including:
- eye damage
- foot problems
- heart and blood vessel disease
- kidney disease
- diabetic ketoacidosis, in which the body breaks fat down as a source of fuel
- nerve damage
However, checking blood sugar levels regularly and keeping them under control using insulin helps to reduce the risk and slow the progression of diabetes complications.
Insulin sensitivity factor and type 2 diabetes
Insulin sensitivity factor assessments are only useful for people with type 1 diabetes who no longer produce insulin.
People with type 2 diabetes may still produce some amounts of insulin in their pancreas, and so they cannot calculate their insulin sensitivity factor reliably.
People should be sure to talk to their doctor to find out what is best for them.
People with type 2 diabetes should focus first on diet and lifestyle changes to lower their blood sugar levels.
After this, a doctor may recommend medications, such as metformin. This works by reducing the amount of glucose the body releases into the bloodstream and makes the body's cells more responsive to insulin.
Find out more about medications for type 2 diabetes:
Diabetes can be a serious disease, but with the correct medication and guidance, a person can live a normal life with this condition and delay the onset of complications.
It is essential to follow the treatment plan and use insulin and other medications as the doctor advises. People should not change their regime without first speaking to their healthcare provider.