Assessing basal insulin

Friday, 25 September 2020

Basal testing allows you to check if your long-acting insulin doses are right for you. Long-acting insulin can also be called basal insulin. This could be Lantus, Levemir, Optisulin, Semglee or Toujeo.

It’s not uncommon to see people taking too much basal insulin. This is a problem as it can result in:

  • Variable blood glucose levels
  • A need to overtreat hypos
  • A need for snacks between meals to prevent blood glucose levels falling
  • Constant worry that you will have a hypo
  • Difficulty managing your weight
  • Difficulty managing your blood glucose levels and exercise

You can check if the basal insulin doses are right for you with a basal test.

This is when you fast (don’t eat or drink anything) for a period of time to see what happens to blood glucose levels when only the basal insulin is working. The idea is for the blood glucose level to be relatively stable.

You should only do a basal test on a day when you’re well. Don’t do a basal test if you’re unwell, or if you have had a hypo in the past 24 hours, are exercising more than normal or drinking alcohol.

Ideally your blood glucose level should be between about 6-13mmol/L before you start the basal test. If it is not in this range wait for another day to do your basal test.

Here are a couple of examples of daytime basal tests:

  • Check your blood glucose level when you wake and have your morning basal insulin dose. Don’t eat breakfast and check your blood glucose every two hours for the next six hours. You can then eat your normal lunch OR
  • Eat an early breakfast, wait for four hours and start your basal test. Check and record your blood glucose level then and then every two hours for the next six hours

If your basal insulin dose is correct for you, your blood glucose level should be within 2mmol/L higher or lower that when you started the basal test. For example, if it was 8mmol/L at the start of the basal test, it should be between 6 and 10mmol/L after the 6-hour period.  If your blood glucose was 10mmol/L at the start of your basal test, it should be between 8 and 12mmol/L after the 6-hour period.

For an overnight basal test example:

  • Eat your evening meal early and wait four hours. Don’t eat any supper. Check your blood glucose level then, as this is the start of your overnight basal test. Set an alarm so you can check your blood glucose level at 3am, and then check again when you wake in the morning.

For the overnight basal test, we’re interested to see if the blood glucose level is relatively stable from the start of the basal test (four hours after dinner) until 3am. From 3am, some people may experience the dawn phenomenon where blood glucose levels rise before waking. Each time point on the overnight basal test is informative.

Your diabetes team can help you assess and monitor basal insulin doses.

By Helen d’Emden

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