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  • Writer's pictureMeg

How to: Basal Testing

Updated: Sep 16

*The information on this blog is not medical advice! It is simply a sharing of my experience of how I basal test. Always work with your endocrinologist or a diabetes educator to adjust medication.

Hi! Want to know probably one of the best tools to increase your time in range? If you can't guess from the title of this blog, it's basal testing. I first learned about basal testing after NINETEEN YEARS with t1d. So hopefully by sharing this I can enlighten some of you earlier in your journey! I have done basal testing with both my endocrinologist during my omnipod pump training, and also with a diabetic health coach that I worked with. Each version was slightly different, so this method is a combined version of what I use for basal testing now.

First thing first. What is Basal Testing?

Basal testing is a process of discovering the accuracy of your basal or background insulin by eliminating factors that may effect blood sugar (like exercise and eating) and evaluating the results. In other words, its a 6-12 hour time chunks without eating or exercise to test how well your basal insulin is working for you.

If you have highs and lows throughout the day, it can sometimes be hard to determine if they were from a miscalculated meal bolus, correction bolus, or basal. Basal Testing confirms your basal settings so you can better explain trends, and then ultimately spend more time in range!

Because there are 24 hours in the day, you can choose to break up the basal testing periods by 6 or 12 hours, or a combination. I typically do a 12-hour test overnight, then two 6-hour tests during the day. The tests are done scattered over a couple of days or weeks and provide you with incredible insights to what's happening. (I also know some people who do it as a 24 hour test-- which is fine, but as you will see in the rules below, that's a 24 hour fast. If that's your thing, go for it! If not, breaking it down into smaller chunks will give you the same results).


There are a few key "rules" to follow to ensure the efficacy of the testing. They are:

  • Do not eat or exercise during the testing period. (And if you're not a regular exerciser, I don't recommend working out 24 hours before the test. You want to know your typical baseline insulin sensitivity.)

  • Do not give yourself bolus insulin during the test.

  • If you drop low or go high during the test, end the basal testing and correct. Then, adjust your basal insulin (instructions in step 5 in the next section) and do the test again another day.

  • Use a cgm or fingerstick to record blood sugar every 2 hours. If you're team fingerstick, you may be dreading getting up every 2 hours to test your sugar. But trust me, one interrupted night is totally worth it to get your basals squared away so you can enjoy every other night thereafter!

  • Don't drink coffee or tea. Water is okay. (For some people, coffee/tea does not effect their blood sugar. In that case, go ahead. But again, just sharing what I do!)

Sound difficult? I promise it's really not that bad. If you time out the tests in the right way you may not even notice the fasting aspect of it.


Here's how I complete my tests. Of course, make this your own. If you want to choose different start times, go for it!

  1. Start with the overnight test. I like to eat dinner before 6pm and start the test at 9-10. That means my last bolus and last meal ends at 6pm, even though the test starts at 9-10. Essentially you don't want bolus insulin effecting your sugar at the start of the test.

  2. Make sure your blood sugar is in range when you start. If it's not, try again another day. It's most helpful to eat a meal that you know how to bolus for for dinner so it's more predictable. (More on meal composition later!)

  3. If you have a cgm, go about your night as usual. If you are fingersticking, test your sugar every 2 hours. (Fingerstickers may want to do two 6-hour overnight tests just to get a better sleep).

  4. Return to normal eating/exercising at 8am.

  5. Check out your patterns. If my blood sugar raised or lowered by more than 30mg/dl, I adjust my basal. This is where I recommend working with your endo or an educator. I personally feel comfortable to adjust mine on my own, so I typically look 3-5 hours before the drop/raise and then make a small adjustment that accounts for that raise. For example, if I went up by 50mg/dl, and my correction factor is 1:50, I would add in ~1 unit of insulin across a few hours.)

  6. If you had to make an adjustment, do so, and then repeat the overnight test. Once you're happy with the results, move on to the next step! See! Not so bad. Here's how I do the other two slots:

  7. A few days later (or weeks, or whenever), I do the morning test. If my last test ended at 8am, I will start this one at 8am. Because it's the morning, I typically don't wake up early to eat. If you wanted to, you could eat a breakfast before 6am, but again, you want to start in range with as little food/bolus insulin impact as possible. So, make sure that it's a predictable meal.

  8. If you have a cgm, go about your morning as usual (but without eating/exercising). If you're fingersticking, record your blood sugar every 2 hours.

  9. Return to normal eating/exercising at 2pm.

  10. Repeat step 5 and 6! Almost done!

  11. Last but not least, it's time for the afterrnoon test! This one starts at 2pm and goes to 8pm. I eat lunch before 12pm, then start the test at 2pm, making sure that I'm in range.

  12. If you have a cgm, go about your afternoon/evening as usual (but without eating/exercising). If you're fingersticking, record your blood sugar every 2 hours.

  13. Return to normal eating/exercising at 8pm.

  14. Repeat steps 5 and 6!

That's it! You've completed you're first basal test!

Here are some more tips to keep in mind during the testing:

  • Meal composition: The meal that I finish 3-4 hours before the testing starts should be something that I know how to bolus for. It should also be something that has whole foods (mainly carbs) and little fat (whole food fats, like avocado and nuts, if wanted). Why? Fat, especially saturated fats and animal products, can cause the delay of a glucose spike up to 8 hours later. So for a basal test, that means the results that we see may not be caused by lack of basal insulin, but actually due to the fat content of the meal. For me, this means a plant-based meal like a sweet potato with black beans, salsa, and avocado. For others, it may still include some animal products, but as a smaller portion and with less oil. Again, you do you-- if you want to eat a sausage pizza before a basal test go for it, but it's probably not going to give you the most accurate results.

  • Recording: You don't need anything fancy to record the testing. Here is an example of what my recording may look like. What you can see on this chart is that there should definitely be an adjustment because I drop 48 mg/dl overnight, despite being in range. That means if I had started with my blood sugar lower, I would have woken up low. We don't want that. How would I adjust this? Because it's a pretty steady drop, I would probably decrease my basals by .05-.1 from 6pm to about 3am, then test again. It's not a perfect science, so there's not one right answer. Small changes can make a big difference, especially over a few hours, so I always start small. And not to sound like a broken record, but endos are a great resource to help you figure this out.

  • MDI vs. Pump: Basal testing is easier with a pump because you can make more precise adjustments. But that doesn't mean that it's not possible to do with MDI as well! When I do basal testing for MDI, I adjust my long-lasting insulin doses by one unit at a time. You can also play with what time you give your long-lasting insulin (because the insulin peaks at certain times, mine peaks around 6 hours after inject) and play around with how to split insulin. Again, endos and educators can help you navigate this.

  • Frequency: I don't do this testing full-way through more than once or twice a year. If I'm noticing, for example, that I am waking up in the morning low, I may repeat just the the overnight test.

  • Period: Your insulin needs may change before and during you period. This is normal! Typically I'm more resistant before my period and super sensitive during. You can do a run through of the full basal testing during your period to see what works, but what I tend do to is just trial and error temp basals. You do you!

  • Alcohol: Alcohol can effect blood sugars, sometimes up to 24 hours after drinking. I don't consumer alcohol 24 hours before the start of a basal test.

To sum it up, I want to emphasize that although this process may feel quite scientific, type one is as much as an art as it is a science. It's less about getting your basals perfect, but more about intuitively understanding what is happening in your body so you can live in more stability-- blood sugar wise.

Okay my friends, that's all I have for you! What's next after getting your basals set? You can then start to explore carb and correction ratios! I'll write another blog on that soon. Together, these tools can help you MAJORLY improve your time in range and a1c!

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