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Basal rate testing

December 03, 2014 by Scott Johnson

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 right. When basal rates are off, it’s like walking through quicksand – doing a lot of work, but making no progress, or in fact, even sinking into deeper trouble.

What is basal rate testing

Thankfully, basal rate testing can help us figure out if we need to make adjustments. However, the name is misleading, as if it’s a simple task on a to-do list. It’s quite involved and a real pain in the ass. And of course, it has to be repeated a few times to make sure 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 cover 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 – it comes from whatever long lasting insulin you use! The only difference is that you’ll have a bit less flexibility when it comes to making adjustments.

Break it down

Because doing a basal rate test involves fasting, it is common to target sections of the day  (so you don’t have to starve yourself for long) and do only one part per day. The most common times might look something like this:

  • Overnight – 10p to 6a
  • Morning – 6a to 12p
  • Afternoon – 12p to 6p
  • Evening – 6p to 12a

These times are not set in stone, of course. The main idea is to cover the entire 24-hour day, testing each of those sections on different days. You’ll also want to test each section more than once, even before making any changes, to make sure any movement you saw in your BG is from your basal insulin. You’ll have to retest each section again after you’ve made adjustments to see if you fixed what you intended to fix.

Have I mentioned 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, I like to start with my overnight test. When it comes to eliminating variables, sleeping works wonders.


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

  • Start with a blood sugar between 80 mg/dl – 180 mg/dl.
  • Your last meal should be at least 4 hours ago, but not more than 12 hours ago (fasting too long can trigger the body to do things that will mess up the test).
  • Not too much fat or protein in the last meal. They can slow digestion so much that it will affect BG’s long beyond 4 hours.
  • Your last bolus (mealtime or correction insulin) should be at least 4 hours ago.
  • No lows in the past 6 hours (due to counter-regulatory hormones).
  • No unusual sports or activity in the past 12 hours.
  • No alcohol in the past 12 hours.
  • No big stress or illness during the test
  • If you use an insulin pump, you might not want to do the test on the first or last day of your infusion set.

Doing the Test

This part is all about collecting data. Try to sail through whatever part of your day you are investigating without doing stuff 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 Logbook) and keep good records. Record the time and result of each test.
  • Check your blood sugar if you feel low. If you are low, 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 too high, stop the basal rate test and correct the high. 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? I would consider anything more than about 30-40 mg/dl of movement something to address. And remember where I talked about repeating the test? This would be a good place to think about double checking. Do you see that same unusual movement again at a similar time on another day? If so, you can be pretty confident that your basal insulin should be adjusted.

What about a CGM?

What if you wear a continuous glucose monitor (CGM)? Do you still have to do all of this testing? In my personal opinion, yes, but maybe not as frequently.

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 so, mix in some regular BG checks to be sure.

With that in mind, a CGM can give you tons of information during pockets of the day or night that will be very valuable for your basal rate testing.

Then the Tinkering Begins

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 valleys, but that is not how a non-diabetic pancreas secretes insulin. Keep your basal profile as simple as possible.

There are two great 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.

I’m sure there are others as well, and I’d love to hear about them – leave a comment if there’s a favorite book or resource of yours that I don’t know about.

On Injections?

This is an area that I’m not very familiar with. I’ve been using an insulin pump for way too long (I started in the mid-to-late 1990’s). In fact, I’d have to do some research to even tell you what all of the current long-acting insulins are today.

That being said, much of what we’ve covered here does still apply to you. 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 with so much information to work from.

Think Like a Pancreas

Another great resource that I feel confident in recommending is “Think Like a Pancreas” by Gary Scheiner, MS, CDE. Make sure you get the latest version, 2nd edition (pictured here). There is an entire section in chapter six about fine-tuning injected basal doses.

Here’s a secret… looks like there are some shortcuts the pumpers don’t get to take. Shhhh! Don’t tell them that!

Cover image of "Think Like a Pancreas" book from Gary Scheiner

Think like a pancreas


What to Shoot For

For most people, basal insulin makes up about 40-60 percent of their daily insulin needs. Though if you eat a lot of carbs you’ll have a lower percent as basal, and if you eat very few carbs 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 of the norm, then, by all means, do what you need to do.

Can Logbook Help?

We’ve added some cool things to the 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.

I’m also a huge fan of the BG Reminders. When I’m supposed to test so often it’s very easy to lose track of time and forget. Having reminders is a big help. You can 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 your blood sugar should stay right where it belongs (most of the time), and you’ll have a confidence that 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, and is a lot of work, and is very inconvenient… But the payoff is totally worth it.


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  • Emma Baird

    Really useful piece – thanks.

  • Scott K. Johnson

    Thanks for stopping by, Emma!

  • Fergal Roche

    Could anyone please let me know in detail how to correct my basal rates which seem to be all over the place.Lows and highs.on paradigm medtronic insulin pump using novorapid as basal and bolus.
    South Kilkenny

  • Scott K. Johnson

    Hi, Fergal!
    Thanks for reading!

    I tried to describe the process in this post – are there parts that are confusing, or that I should clarify more? It all comes down to fasting and eliminating variables so you can see if your basal insulin is doing what you expect. Then, if it’s not, making a small change and trying the test again.

  • Danny

    “Last meal not more than 12 hours ago.” This is impossible for testing the 6am-12pm window. Unless one has dinner at midnight.

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