Interpreting overnight basal test


Welcome to the world of FUD. I’ve rapidly gone from “Do what the CDE says” to “Let’s try something new.”


Maybe wake up to do a fingerstick at the midpoint? But then that could cause a wake up spike if you’re prone to them.

My explanation for why I don’t think this will cause a problem will get pretty far down in the weeds. And I might not even be correct. Maybe we’ll save that for another time after you decide what you want to do tonight.

If you reduce your basal by 5% across the board, that’s removing 0.46 units of insulin over the course of 10 hours.

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For us, it is not possible to compare a basal unit with a bolus unit: a basal unit is worth a lot more than a bolus unit in mg/dl for us. To give you an idea, 5% across the night would result, for us, in a difference of about 100-125 mg/dl. Again, YDMV :slight_smile:

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That just means type faster.

ha ha ha


Totally agree and understand that!

This might be a difference in women’s physiology. Maybe not. But if I had that Dexcom graph that Larissa had last night, a 5% decrease would level it for me. I cannot say what a 5% change DURING Week 2 would do to my graph since I’ve never tried it (bc no need). Maybe if I feel sporty one day I’ll give it a whirl for science.

Maybe we’re also coming from different experiences of deciding between basal rate changes hour to hour vs scaling the whole thing up or down slightly. If the big picture all trends down, every hour for me has too much insulin. If I have dips or spikes, I need to zero in on the actual hourly basal rate that is set too high or low.

I just don’t want to overwhelm @LarissaW! Sorry!


I feel for me it will be a combination of these two thought philosophies, considering these points:

  1. I am guessing that my basal affects me more quickly than others because of the FIASP’s quick action timing
  2. Overall I feel I am dropping too much from when I put my head down to when I wake up
  3. That drop seems to be most prominent earlier in the night (10-1) and exacerbated by later in the night

Taken that together, looking at my current settings:

I am thinking of dropping them across the board as follows:
|8p-9p: .95|
|9p-12a: .95|
|12a-2a: 0.8|
|2a-3a: 0.825|
|3a-6a: 0.875|

That way the changes aren’t anything drastic in its individual time frame but additive might balance me out?

I’m going to have to take a guess at this and test it I’m realizing :woman_shrugging: If I end up high one night I’ll be fine (I used to be a pro at it!)

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With the kind of overall drift down that we’re seeing in your graph overnight, I’d be making a quite small
decrease in basal. Like 0.025u per hour, and see what that does. In my case that might completely fix it, or maybe the next night I’d drop it again by another 0.025 if the overall trend is still down.

In your first graphs it looked like 10pm to 2am was the trouble time, but in the second graph it was more or less all night long. So it’s helpful to watch for several nights in a row to see what’s the common trend, and with really small changes like 0.025u I can see the overall trend changes without getting thrown off by the variation from day to day.

For Humalog I generally start the basal change 1.5 to 2 hours before I want it to take effect. So in your case with Fiasp, maybe 1 hour ahead is reasonable. The idea is to prevent a BG trend change before it happens, rather than trying to catch up to it after it occurs. Recall that if you change the basal 1 hour ahead, the effect isn’t immediate. The change in active insulin in your bloodstream accumulates over time because the insulin is delivered over time, comes into effect over time, and tails off over time.


Ah gosh. I’m sorry I hadn’t posted here with updates. However, I made these changes to basal

I didn’t have any more good days within that week in my cycle to officially do an overnight basal test, but I noticed overall that I am stable overnight, and have gotten rid of my dipping trends overnight. That being said, I also have NOT gotten any upward trends (that were not from underbolusing from dinner) (like @Michel thought might happen from too much of a decrease in overall basal, based on their varying sensitivities to BASAL vs BOLUS). So, overall - the slight changes of dropping overnight basal in each time frame (as suggested by @T1Allison) seem to have worked for me. YDMV

I plan to do some more overnight basal testing when I’m back to week two to confirm the trends I’ve noticed.

Now I’m curious if basal changes affect males and females differently and if there’s overlap in both types of physiology in certain times during the female cycle.

Also since it’s been a topic in this thread, I’m planning on experimenting a bit to figure out how long it takes for basal changes to affect my blood sugar with FIASP


Thanks for letting us know how it went! I’ve been wondering!! I’m glad your modest tweaks across the board helped stabilize you in Week 2!

Me, too.

As you probably know, I am a woman in my reproductive years and have not yet reached perimenopause. I have observed my own patterns for years and kept lots of notes. I want to pass this along to hopefully give you some things to look for to see if they behave similarly for you (or any other reproductive aged woman reading this). Note that my personal bg ranges are what I use to keep me safe since I experience bigger sensitivity fluctuations now that I am no longer on birth control. FWIW, and a Big YDMV here, the following are the indicators I use for safely adjusting my basals in response to hormone-induced insulin sensitivity changes each cycle:

  1. In general, individual spikes and dips (greater than 30 points) indicate an incorrectly set basal rate at a specific point in time. This alone would not make me think that hormones were causing a big picture problem.
  2. In general, here are the five main scenarios I look for in reviewing fasting bg’s (typically looking at overnight numbers on my Dexcom) as they relate to insulin sensitivity changes due to hormones:
    a. level bg AND within my ideal range (somewhere around 100 is great in my book): Yay! My basals are working for my current insulin sensitivity! Leave it alone!
    b. level bg BUT higher than my ideal range (once it is stuck level at 150 or above for my safety parameters): Hmmm. My basal rates are strong enough to keep me level, but not strong enough to keep me level near 100. Add 5% and see what happens.
    c. level bg BUT lower than my ideal range (lower than 80 for my safety parameters): Hmmm. My basal is keeping me level but too low, I’ll try removing 5% and see what happens.
    d. steadily climbing bg: My basal is not strong enough to keep me level. I will need even more basal than a “level but high” basal setting. At this point, I’ll add another 5% for 12-24 hours to see what it does. [Also, I pay attention to if I might have a site issue or oncoming illness. Although I play the “wait and see” game on making basal adjustments for accommodating hormones, I obviously take stronger actions if my bg is in an unsafe range. I will change pods, etc.]
    e. steadily dropping bg: My basal is too strong to keep me level. I will need to drop my basal to try to find where it will stop dropping, and then evaluate what is best for my ideal leveling point (shooting for 100).
  3. I eat the same breakfast every morning. This gives me an early warning system that hormone resistance is cropping up. When 3 units typically works for me, but then I have to start correcting bc it didn’t do the full job…that’s when I know to start preparing for hormone resistance before I even see it in my fasting bg’s overnight.
  4. I keep notes on a cycle basis and check my hypothesis for a given day against what’s worked the last few months. If there is a big discrepancy between what I currently need and what I’ve been needing the past few months, odds are good there is another issue to diagnose, such as a site going bad.

All of this is shared in the spirit of helpfulness. I hope it’s not overwhelming. These are the indicators that work for me in making the “correct” adjustment as quickly and safely as possible.

Basal Rates and Hormones
Ideas for Interpreting Female Basal Testing Results on CGM when Considering Hormones (Insulin Resistance)

@T1Allison THANK YOU.

I’ll be reading your basal rates and hormones thread soon I promise I promise!


I hope this info is helpful for you! I’ll be curious if over time it seems to apply to you, too.

No worries, at all. Those threads have great info in them and are a great resource (IMO), but discussing this stuff real-time with you is totally fine and useful in its own right! If anything I’ve learned through lots of trial and error can help someone else, that just absolutely makes my week!

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I’ve done a few basal tests the past few days for overnights to confirm the stable trends with my new settings, and I’m really really happy that my overnights are now stable consistently (and that I’m getting better sleep :raised_hands:t2::raised_hands:t2:)




Very nice!


Beautiful, Larissa! That is a super job!