How To Successfully Test Your Basal Rate

Why is basal rate testing so important? Because the foundation of our diabetes management is basal insulin.

If our basal insulin isn't adjusted properly, nothing else works properly. When basal rates are off, it's like walking through quicksand – doing a lot of work without much progress, or sinking even deeper into trouble.

What is Basal Rate Testing?

Basal rate testing can help us figure out if we need to make adjustments. However, the name is misleading and makes it seem like a simple task on a to-do list.

It’s quite involved and can be a real pain in the neck. And of course, it has to be repeated a few times to ensure the results are accurate.

Why is it such a pain? Because this test is all about eliminating variables so you can be confident that any changes you see in your blood sugar are a result of your basal insulin.

Eliminating variables? In diabetes? Ha! Good luck with that, right? But don't worry, we'll break it apart into simple basal rate testing instructions. But first, let's go over some basic info and preparation steps.

Not Just For Pumpers

You might only associate basal rate testing with insulin pumps, which is understandable! “Basal Rate” is a phrase typically associated with insulin pumps.

But for those who are injecting, you also have a basal rate from your long-lasting insulin! The only difference is that pen based therapy offers a little less flexibility when it comes to making adjustments.

Break It Down

Because doing a basal rate test involves fasting, it’s common to target particular sections of the day (so you don't have to starve yourself for too long) and focus on one section per day.

Doing everything in one go might sound practical, but often leads to inaccurate results. Your body goes into starvation mode and builds ketones that weaken the effects of insulin.

The most common way to split the test is across four sections: morning, afternoon, evening and night.

Recommended testing times:

• Morning - 6am to 12pm
• Afternoon - 12pm to 5pm
• Evening - 4pm to 10pm
• Overnight - 10pm to 6am 

These times are not set in stone, of course. The main point is to cover an entire 24-hour day, testing each of these sections on different days.

You’ll also want to test each section more than once, even before making any changes, to ensure any movement you see in your BG is from your basal insulin. You’ll have to retest each section again after you’ve made adjustments to see whether you’ve fixed what you intended to fix.

Did we mention that basal rate testing is a lot of work?

Remember, the focus of each section is to eliminate as many variables as possible so that any changes you see are from your basal insulin. Because of this, we recommend starting with an overnight test. When it comes to eliminating variables, sleep works wonders.

Preparation

As you prepare, there are a few things you’ll want to keep in mind:

• The starting sugar should be between 90mg/dl - 180mg/dl (5-10 mmol/l).
• The test should only be performed when glucose levels are stable. (for CGM and FGM carriers: horizontal trend arrow)
• No meal and insulin administration
  → in the last four hours when using a short-acting analog insulin.
  → in the last six hours when using a normal insulin.
• Last meal before the test should be low in protein and fat.
• No values below 70 mg/dl (4 mmol/l) at least six hours before
• No unusual sporting activity 12 hours before
• No alcohol 12 hours before 
• Ensure physical well-being (no strong stress, no infections, fever...)
• If your blood glucose levels fluctuate before menstruation, it is better to perform the basal rate test after menstruation.

Conducting the Test

This part is all about collecting data. Try to sail through whatever part of your day you are testing without doing anything that would affect your blood sugar (no problem, right?). Don't forget to write it all down.

• Don’t eat anything! This is hard but doable. Remember, you’re only attacking a short section of the day. Once you’re done, you can eat all you like.
• Check your blood sugar every hour (tip: set a timer, alarm clock, or use the reminders in the mySugr Logbook) and keep good, detailed records. Record the time and result of each test. If you’re using a CGM, this isn’t necessary. However, you shouldn’t do the test right at the beginning or end of the wearing period of your sensor. 
• Check your blood sugar if you feel low. If you are low, i.e. if your values are below 70mg/dl (3.9 mmol/l), stop the basal rate test and treat the low. Depending on how far into the test you are, you’ve just learned something very useful about your basal insulin!
• If your blood sugar is rising rapidly, i.e. if your values are above 250mg/dl (13.9 mmol/l), stop the basal rate test and correct the high with short-acting insulin. Don’t get frustrated! Again, you’ve learned something useful.
• No unusual physical activity during the test.

After the test (and after you get some food!) take a look at your data. Any unusual movements in your blood sugar? Anything more than 30-40 mg/dl (1.6-2.2mmol/l) of movement may be something to address.

And remember when we talked about repeating the test? This would be a good time to think about double-checking.

Do you see the same unusual movement again at a similar time on a different day? If so, you can be fairly confident that your basal insulin should be adjusted.

Here are a few more tips for the evaluation:

Remember that these are general recommendations. Every person’s diabetes therapy is individual and changes should always be discussed with your doctor.

• If your blood sugar values rise more than 30mg/dl (1.6 mmol/l):
  - pen therapy: increase your basal insulin dose by 5-10%
  - insulin pump: increase your basal rate by 10-20%
• If your blood sugar values sink more than 30mg/dl (1.6 mmol/l):
  - pen therapy: lower your basal insulin dose by 5-10%
  - insulin pump: lower your basal rate by 10-20%
• The basal insulin supply should make up about 50% (with a variety of 40 to 60%) of their daily total amount of insulin. That’s not the case? How about a basal rate test? 
• By the way: People with an insulin pump can easily track their basal rate in the mySugr app and see it clearly visualized in the graph on the home screen.

What About a CGM?

What if you wear a continuous glucose monitor (CGM)? Do you still have to do all of this testing? In our opinion, it’s still a good idea, but frequent testing isn’t so necessary.

CGM’s provide a very useful layer of information, but they do not measure actual blood glucose. They measure something called interstitial fluid, which has a close relationship to the amount of glucose in your blood, but it’s not the same thing.

When it comes to adjusting your basal insulin, you want your test results to be as reliable and accurate as possible. With that being said, a CGM can ease the pain of basal rate testing as long as it’s tracking accurately. In the end, the decision is up to you.

Do you trust what you see? Even if you do, mix in some regular BG checks to be sure. With that in mind, a CGM can give you lots of information during pockets of the day or night that will be very valuable for your basal rate testing.

Let the Tinkering Begin

Your first instinct will be to make big sweeping changes in your basal insulin. Don’t do it! Take it slow and easy, and talk things over with your doctor or care team.

It’s pretty typical to apply small changes, usually 10% or less, and then see how it goes. It can be a real test of your patience to make changes so slowly, but it’s better than making big changes that can goof you up. Better safe than sorry, especially if your conclusions from the basal rate test were wrong.

On a Pump?

Making very specific basal rate adjustments is one area where pump therapy really shines. With an insulin pump, you can program very different basal insulin amounts for each hour of the day (or more).

There is a time-shift involved with basal settings on an insulin pump. To see a change in blood sugar at noon, you have to adjust your basal rate at least 60-90 minutes before.

It’s also very tempting to “over-tweak” your basal profile just because you can. A basal profile can become very complicated, with multiple peaks and lows, but that is not how a non-diabetic pancreas secretes insulin. Keep your basal profile as simple as possible.

There are two books that cover this (and a lot more) in greater detail: "Think Like a Pancreas" by Gary Scheiner, MS, CDE, and "Pumping Insulin" by John Walsh, P.A. & Ruth Roberts, M.A.

There are definitely others as well! We'd love to hear about them - let us know if you’d like to share a favorite book or resource!

Basal Insulin For Pen Users / PWD On Injections

Consult with your doctor: 

• How long is your basal insulin acting?
• Are there any gaps in the basal insulin supply?
• When do peaks occur? 
• Can the injection time be postponed?

If you present all of the data and information you’ve collected to your diabetes care team they might give you a big kiss! Making adjustments will be much easier for them having so much information to go off.

What to Shoot For

For most people, basal insulin makes up 50% (with a variety of 40 to 60%) of their daily insulin needs. Having said that, if you eat a lot of carbs you'll have a lower percent as basal. And if you eat very few carbs, you will have a higher percent as basal.

But remember, you are not “most people.” You know yourself best, and if your data backs up the need for something outside the norm, then, by all means, do what you need to do.

Can mySugr Logbook Help?

We've added some cool things to the mySugr Logbook that we think will help:

• Insulin pump basal profile in the settings and daily graph.
• Insulin pump basal amounts shown in the PDF report.
• Percentage split between basal/bolus shown for each day in the PDF report.
• Percentage split between basal/bolus shown for each time period in the analysis screen.
• CGM data in the graphs and PDF report.

The BG Reminders are also a huge help if you have to conduct tests often. You can also use a traditional timer or alarm clock for this part, but it's much less fun.

A Solid Foundation

Having your basal insulin programmed properly will give you a foundation of stone rather than sand.

You’ll easily spot problems with your meal or correction insulin that may have been camouflaged before, and you’ll be able to get those fixed too.

You’ll sleep better knowing that your blood sugar should stay right where it belongs (most of the time), and you’ll have a confidence you may not have felt before.

Knowing you’re standing on solid ground can do a lot, as can knowing that you have the skills to figure out what needs to be done (and even a little practice doing it). It's all quite empowering.

There's no getting around the fact that basal rate testing is hard, a lot of work, and very inconvenient... But the payoff is totally worth it.

Sources:

Rosak C et al, Angewandte Diabetologie 5. Auflage, 2014

Subito and Flash education programme

Thomas A, Kolassa R, Sengbusch v. S, Danne T, CGM interpretieren, 2017, 1. Auflage

Walsh J. Roberts R, Carma C, Bailey T, Using Insulin, 2003

This article has been updated in September 2020.