Basics of Basal Testing


It would be amazing if figuring out how many unit of basal insulin needed for people with diabetes were as simple as just “doing the math.” But because diabetes is different for every person, basal insulin needs are also unique. Here are some tips on how to best match your basal rates to the needs of your body.

What is basal insulin?

Basal insulin is the background insulin that the body needs to meet normal metabolic needs. The human body normally uses glucose that has been stored in the liver to give the cells the energy they need while you are fasting or not eating. The other type of insulin people typically take is called “bolus” or “meal time insulin” (think “bolus for your bowl of soup”). Although most people do not need day-by-day changes in their basal insulin, there are various times in life where the body’s basal insulin needs some tweaking.

Where to begin

When people first start on insulin, the equation that health care providers use is 0.5-1 unit/kg of insulin for the total daily dose (TDD). (2.2 lbs = 1 kg) The range is used so that if someone is very sensitive to insulin, they use the smaller amount, and if someone is very insulin resistant, the larger amount is used.

Typically, about half of the total daily dose is used for basal and half for bolus. It’s always best to err on the side of caution and start out with less aggressive insulin dosing. Some people are on ratios of 30% basal, 70% bolus, or vice versa. If you’re having erratic blood sugars and are looking for a fresh start, the 50-50 ratio may be the best jumping off point.

How to do basal testing

Since the basal insulin is supposed to match the body’s fasting needs, you have to fast (aka not eat for several hours) to test the basal. The awesome news is checking the overnight basal is pretty easy, you can just skip breakfast or sleep in to see what happens to your blood sugars in the morning.

If you have a continuous glucose monitor (CGM), it is really easy to check this data. If you do not use a CGM, you would check your blood sugar before bed and first thing in the morning. Daytime basal testing can be done by skipping other normal meals and monitoring how the blood sugar reacts. You will want to check your blood sugars every couple of hours during basal testing.

You want to make sure that you are starting out at an in range blood glucose level before starting any basal rate tests. For example, if you check your blood sugar before bed and you need to take a correction bolus, it would not be the best time for a basal test. The goal is to have no bolus insulin, food, or exercise active in your system, and then do your basal testing!

Why would I want to do basal testing?

Basal testing is recommended if you are:

  • having blood sugar fluctuations that are surprising or irritating and you want to figure out a solution.
  • starting a new routine or schedule
  • switching from injections to a pump or vice versa
  • waking up with blood sugars that are consistently out of target range
  • looking for more data about your insulin needs

When are some common circumstances when basal needs change for people?

  • during puberty
  • pregnancy
  • end of honeymoon phase
  • perimenopause or menopause
  • weight change (loss or gain)
  • normal age-related changes

For more information on how to do basal testing, PWD powerhouse and CDCES Gary Scheiner has a great write up.


Clinically reviewed by Marissa Town, RN, BSN, CDCES