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Scott Johnson


January 22, 2014

Basal Rate Testing

January 22, 2014 | By | 27 Comments

Highs and lows are a normal thing when living with diabetes. We can’t expect to have perfectly smooth blood sugars everyday. But there are things we should watch for and sometimes there are small adjustments that can make a big improvement.

You need to have a strong foundation to do much of anything else. In our case, that foundation is basal insulin. If our basal insulin is not adjusted properly, nothing else works right. I think of it as walking through quicksand – doing a lot of work, but making no progress, or in fact, even sinking into deeper trouble.

Basal Rate Test

There is something called a “basal rate test” that can help us determine if we need to make adjustments. The name is misleading though, as if it’s a simple task on a to-do list. It’s actually 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?

Not Just for Pumpers

“Basal Rate” is a phrase typically associated with insulin pumps, which might lead to the idea that basal rate testing is just for those using a pump. That’s not the case. For those who are injecting, you also have a basal rate. It comes in the form of 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 a specific section of the day  (so you don’t have to starve yourself for long) and do only one section 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 main focus in 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 does wonders.


As you prepare for your basal rate test 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 Companion Pro) 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 are not measuring 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 exact same thing.

Have you ever experienced a large difference between what you see on your CGM and what a traditional blood sugar check shows? I have.

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 really 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.

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 very small changes, usually 10% or less, 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 really goof you up.

Better safe than sorry, especially if your conclusions from the basal rate test were wrong.

Red Pill or Blue Pill – Choose Here…

  • Making very specific basal rate adjustments is one area where pump therapy really shines. With a 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.

  • 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!

    tlap 2 

What to Shoot For

For most people, basal insulin makes up about 40-60 percent of a 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 Companion Help?

We’ve added some cool things to the latest release of Companion Pro 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

Basal Info on 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 my diabetes monster remind me 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.


  1. Hi Scott,
    Great article. I don’t think I have ever done a proper basal rate testing. Just looking at the time frames involved I’m not even sure where to start. 10PM to 6AM seems ideal unless, of course, I want to get a good night’s sleep. I tried it once on a weekend but getting up every hour and reseting the alarm was too exhausting. I’m not a night person. I starting falling asleep on the couch at 9PM and get up daily at 6AM.

    Is this really important? Looking at the other suggested times I feel this would be impossible for me to do without getting a hunger headache.

    • Hi Khürt!

      Thanks for taking the time to read my super long post! :-)

      Maybe your overnight basal test window would run from 9pm-6am? Customize those time windows that I listed to best fit your lifestyle, with the goal being that you cover the entire 24-hour span eventually. For example, maybe you take a few days over the next two weeks to get your overnight basal really dialed in. Then pick another section to work on – wake up and skip breakfast to look at that section of the day. Do that a few times over a couple of weeks, etc.

      It might take a while to cover the entire 24-hour day, but who says you need to rush? You get to make the rules, right?

      The part about not getting a good night’s sleep might be unavoidable though, depending on whether you trust your CGM (if you use one) to report accurate information. When I do mine, I’ll be waking up for a quick fingerstick test a few times through the night, just to be sure.

      As far is it being important? Again, it’s a decision you have to make for yourself. If you feel pretty good about your basal rate settings, then it may not be worth the effort. I personally haven’t looked at mine for a very long time, and feel there’s a lot of room for improvement, so I feel that doing a series of basal rate tests would be worthwhile for me.

      Another approach you might take is doing more sections of the day, but make the sections smaller, so you don’t have to fast quite as long. The important part here would be to make sure you’re giving everything enough time to “wash out” from previous meals and boluses. Does that make sense?

      I hope that helps, Khürt! Thanks again for stopping by to read! Happy to chat more about it, too.

  2. Thanks for writing about this, Scott!! I have been meaning to do this for quite some time.

    • Thanks for reading (and sharing), Manny! I tested the other night and found some adjustments I need to make. I’m hoping to get back to it again to confirm in the next week or so.

      Keep us posted if you do yours, too! I’d love to hear how it goes!

  3. Janeen

    Thanks for typing all of this out and sharing it with us. If they had their ways, my nurse practitioner and doctor would most likely have me do this once a month forever (once a month for 3 consecutive days during breakfast or lunch or dinner or overnight, choosing a different time period to check each month). They don’t require me to test every hour IF I’m wearing my CBGM, but I do still have to calibrate it BD p1during the testing time periods as I would any other time.

    I personally HATE doing basal rate checks. I know they’re important, but does anyone have any suggestions for something safe to kill my appetite during rhis testing? It’s very hard to be at work and not eat when all of my coworkers are eating. My appetite is bad enough without skipping meals, and it’s, unfortunately, very hard for me to complete these tests successfully most of the time. I literally have to sleep in the evening for 3 nights in a row when testing during dinner time because I’m so miserable. Perhaps most people could just skip dinner, go to bed and be fine sleeping till breakfast, but not me. I will get up and eat when testing is over around midnight. So not healthy.

    I am open to ideas and suggestions, not including wiring my mouth shut (although I have considered it!). In my opinion, this is one of the worst parts of being diabetic. I would love to not ever have to do it again. I appreciate everyone’s time. Thanks,


    • Hi Janeen!

      Thanks for such a thoughtful comment and your great questions. I think many of our HCP’s would love us to do these much more often that we do. You’re so right though, they are a royal pain in the butt.

      One thought I have is maybe breaking the segments into smaller pieces so you don’t have to fast for so long. It might mean eating meals at weird times, but who cares? I’m also of the same opinion of your eating after the evening segment – makes perfect sense to me, and I’d probably do the same thing! I am not personally worried about eating then going back to sleep not being healthy because it’s not an everyday thing. For the few times that you have to do that segment, do what you gotta to, you know? And which is the most bad? Eating and then going back to sleep, or trying to fast for such a long time? There could be a strong case made for either, I bet!

      Keep in mind, I’m not a trained medical professional, so nothing I’m saying here should be considered anything more than just another PWD’s personal opinion. And you know what they say about opinions, right? They’re just like … armpits. Everybody has them. :-)

      Let’s hope we get more thoughts here – I’d love to hear what others think about all of this.

      Thanks again, Janeen!

  4. Leah

    This is so great Scott! What detailed information. I ‘bookmarked’ this for future use and/or in the case my Endo. and I feel like I need to do this after my appointment. Thank you for shedding light on an area of my bg control I truly didn’t know much about. You are good at communicating about this stuff and I love how honest you are about how ‘un-fun’ it is but still worth it! Keep on being awesome friend.

  5. Thanks for this very informative post, Scott. Reminds me, too, that I’m way overdue for basal rate testing at all times of the day and night. Sure, I know how just from doing it through the years, but it’s really nice to get the rundown like you have in your post here. And there’s a handful of things that I’ve kind of glossed over in the past when doing these, and need to take more care of considering. Now that I’m on the G4, it’s a great time and I’m going to print this out and use it in my tweaking. Thanks again for writing this, my friend.

  6. I have dawn phenomenon, and use 9 basal rates to null this out. I got all the rates set quite well using the freestyle navigator CGMS.
    Support for the Navigator was withdrawn two years ago, I’ve been “coasting” since then. My current insurance won’t cover cgms, since “I am doing so well without it” (5.3). I have little knowledge of how accurate my overnight basal rates are, I have insomnia and take sleeping pills.

    (Thanks for allowing me to vent) LOL
    Very nice article Scott. I miss both the mutual friends we just lost.

    -Lloyd Mann

    • Thank you, Lloyd. I miss the Navigator, too! And boy, I can’t imagine trying to do any overnight basal rate testing while on sleeping pills. But then again, with an A1c like that, it’s probably not a big issue for you.

      And yes, it’s been a rough week in terms of lost loved ones. Thanks for stopping by and taking the time to leave a comment. I appreciate it.

  7. Scott, what an excellent read! I have just been changing my eating habits and changed my basal rates rather quickly. With your explanation, I fear it was too quickly as 2 weeks later when I introduced certain a food categories back into my diet, it was all over the place.

    I’m thinking it could have been my insulin:carb ratio. Luckily I’m seeing my doctors at the hospital on Monday to this through with them.

    Thank you


    • Hi Sabbz! Thanks for reading!

      How interesting! I’d love to hear how your appointment goes and what they think of it.

  8. The part about the CGM may be inaccurate. CGM’s are generally fairly accurate with trending. The purpose of a basal test is not what the actual glucose numbers are but the rate of change of those numbers. So if the CGM says I dropped 1mmol/L(18) in an hour, I can be confident in that number.

    • Good point, Darrell, thanks for chiming in!

      • Also, the 60-90minutes is a fun one as many things affect it like activity, heat, scarring, and dose amount.

        • Phase of the moon, which side of the bed cookie monster woke up on, whether the wind is blowing from the east or west, and more… so many things…

  9. Hey Scott, thanks for the article. I Googled “basal testing” and this was on the front page. Great work with the metadata! This is a very valuable article, and I’m going to share it in my local T1D group here in the Quad Cities.

    • Thanks, Rich! I always appreciate your kind words and awesome support!

  10. Tavia

    This is very nicely written, Scott!

    I like that while you list the “rules” of basal testing you also explain the rationale for the rules with real world examples. I’m planning to use a few phrases from this post while training CDEs and providers on how to verbally explain basal testing when we give people our handout that is mostly “just the facts.”

    Thank you for posting!

    Whenever I see (more than the normal amount of) squirrelly stuff, I go back to basal testing. Sometimes I need a little nudge from my NP friend who I consider to be a Basal Testing Queen since she recommends it so often. Because it works. :-)

    Aside from overnights, I always do smaller windows of time because as someone posted above: the hunger factor kicks in during the waking hours.

    While adjusting basals do not lead to flat line BGs 24/7 for me (of course), I absolutely get the benefits you listed. And I do get a lot of ‘flat’ lines overnight which is awesome!!

    • Hi Tavia!

      Thanks for reading! I’m so glad to hear that you find it useful, and am thrilled that you find it useful enough to help teach! :-)

      I love the point you make about being able to break things down into smaller windows of time – that’s a great way to make it work well for your personal situation. Thanks for echoing that!

  11. Comfy

    Interesting .
    l wld want to do this .
    Thanks for sharing.

  12. Andy

    Hi Scott !
    Great article… I am just doing basal testing… last three weeks and I hope I am done by end of this week… I knew all the rules, problem is that I was changing wrong basal rate entries… In your article you state that timeframe changed should be 60 – 90 minutes before BG was faulty… I changed always basal rate one hour before “faulty” BG, but reading in Walshes book, changed basal rate should that that comes 90 – 120 minutes before bad BG.
    Otherwise great article…

    • Hi Andy!

      Thanks for reading and taking the time to share your thoughts! You’ll be one finely tuned machine when it’s all said and done – that’s wonderful! Please let us know if the timing change continues to make the difference for you. Some of the resources say 60 minutes, others say 120 minutes, and some 60-90 minutes. Like many things with diabetes, it seems to vary quite a lot between individuals and we have to try something and see what works best for our unique situation.

      Keep us posted, and here’s hoping for flat lines and smooth sailing! :-)

  13. I was wondering what program/app is shown here…..

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