People with type 1 diabetes will require lifelong insulin from the time of diagnosis, unless they experience "honeymoon period" with occurs temporarily soon after diagnosis or they had a successful islet or pancreatic transplantation. Otherwise, insulin treatment is an essential part of living with type 1 diabetes.
The main difference between insulin treatment for type 1 and type 2 diabetes is the absence of residual beta cell and endogenous insulin in people with type 1 diabetes. This makes them more susceptible to hyper- or hypoglycaemia with inappropriate insulin doses. Furthermore, insulin dosing for people with type 1 diabetes also needs to be matched with carbohydrate intake to avoid glucose fluctuations.
This process of optimizing insulin doses accurately requires:
1. Education and training from the diabetes care provider team
2. Practice by the person with type 1 diabetes
3. Frequent monitoring of blood glucose, especially using a sensor
4. Revision of insulin doses by the diabetes care provider team
The main types of insulin prescribed for people with type 1 diabetes are the long-acting basal insulin and a rapid (or ultra-rapid) acting prandial insulin. The dose for long-acting basal insulin is similar every day, and adjusted based on need to aim a fasting blood glucose within goal while avoiding nocturnal hypoglycaemia. On the other hand, the dose for rapid-acting prandial insulin needs to be matched with carbohydrate intake, and may vary from day-to-day.
A common way to prescribe rapid acting prandial insulin is by using insulin-to-carbohydrate ratio (ICR) and insulin sensitivity factor (ISF, also known as correction factor). ICR is the ratio of carbohydrate (in grams) amount covered by 1 unit of rapid-acting insulin, while ISF is the amount of blood glucose (in mmol/L) brought down by 1 unit of rapid-acting insulin.
For example, a person with ICR of 10 and ISF of 4 who plans to eat 2 slices of bread (30 gram of carbohydrate) and a pre-meal glucose of 10 mmol/L will require 3 units of rapid-acting insulin to cover for 30 gram carbohydrate intake, and an additional 1 unit of insulin to bring down pre-meal glucose from 10 mmol/L to 6 mmol/L.
Although there are mathematical equations to estimate initial ICR and ISF based from total daily insulin doses, over time ICR and ISF needs to be adjusted by the diabetes care team based on glucose control and glucose fluctuations, similar to basal insulin adjustments.