Overnight basal

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JohnWhi

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Type 1
Since I started the Freestyle Libre trial in January, I have been trying to tackle the following phenomenon: although finger-prick BG readings are OK before bed and on waking, I seem to have rather low interstitial glucose readings between midnight and 4am. (When I have woken to check BG, I have not found them significantly low, but that is another matter.) On advice from the clinic, I have been gradually reducing the basal rate from 0.5 units/hour in January to 0.1 units/hour now. The problem is that the readings are now fairly similar to when I started. In fact, when I paused basal and fell asleep, waking only with the bleep of the pump at about 5.15, the reading had not risen. On the other hand, the basal requirement has become greater from 4am to 8am, 0.8u/H when I started, 1.3u/H now. Is it logical to conclude that, at night, changes in the basal rate take some hours to have an effect? The 4am to 8am increase seems to correspond broadly to reductions made from 10pm to midnight and midnight to 4am. During the day, pausing basal seems to have an effect in an hour or so. Have others noticed a similar phenomenon of delay in effect at night?
 
I don’t think it’s that changes in the basal rate timing differ. Rather, I think it is the fact that your liver differs in how much glucose it is trickling out.
I’m not on a pump, so take a flat basal overnight, and I always have what I term my 'washing line' effect. My levels fall steeply just after I’ve gone to sleep, and round about 3am I level off, then start to rise until I’m the same as when I went to bed.
If I sleep really well, sometimes it’s less pronounced, but if I’m stressed and start waking around 4am and worrying about what’s stressing me, my BG shoots up. Hence I think it’s my liver springing into action to gear up for the day ahead.

And on your other point about Libre readings I always find mine read lower at the bottom end, so it’ll put me in the red at 3am, whereas if I wake and test, my meter will have me between 4 and 5.
 
Many thanks for your response, Robin. The point about the liver probably explains why, after making a reduction in basal rate, my level seems to hit the deck. Your "washing line effect" is reassuring. I have contacted the pump clinic and am told that the consultant will respond with advice.
 
Update: I have had a very prompt answer from the consultant. She tells me I am correct in thinking that a change in basal rate takes a number of hours to take effect and suggests one makes the change at least two hours before the point at which one wants it to take effect. We live and learn!
 
JohnWhi said:
Since I started the Freestyle Libre trial in January, I have been trying to tackle the following phenomenon: although finger-prick BG readings are OK before bed and on waking, I seem to have rather low interstitial glucose readings between midnight and 4am. (When I have woken to check BG, I have not found them significantly low, but that is another matter.) On advice from the clinic, I have been gradually reducing the basal rate from 0.5 units/hour in January to 0.1 units/hour now. The problem is that the readings are now fairly similar to when I started. In fact, when I paused basal and fell asleep, waking only with the bleep of the pump at about 5.15, the reading had not risen. On the other hand, the basal requirement has become greater from 4am to 8am, 0.8u/H when I started, 1.3u/H now. Is it logical to conclude that, at night, changes in the basal rate take some hours to have an effect? The 4am to 8am increase seems to correspond broadly to reductions made from 10pm to midnight and midnight to 4am. During the day, pausing basal seems to have an effect in an hour or so. Have others noticed a similar phenomenon of delay in effect at night?
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Hi John

We each need different amounts of insulin, which is why the pump comes into its own overnight. Just one thought, I was not sure whether you did any fingerprick checks during the night, along with the Libre profile. I had a couple of nights where the Libre had flatlined as all, but I concluded that it was me lying on it directly.
I am not sure that that fits with what you have described, but it might be worth an alarm and a check in the night.

I hope that you can get things sorted.
 
Thanks for the suggestion SB2015. I have done this on a number of occasions and it never indicated anything too low. There again, I have had divergence of "LO" on the Libre and 6.5 on the fingerprick, 4.5 on the Libre and 12.8 on the fingerprick. These are extremes and one is not measuring the same thing. Most of the time there is not too much difference. (Interesting article by Roderick E. Warren in Diabetologia on the divergence.) As you suggest, the consultant said I might be lying on the sensor, but the last Hba1c was identical on Libre and on the blood test, so we decided to go with the Libre reading. It has even been suggested that the CCG would like me to do fewer fingerpricks, but this comes up every few years and I tend to ignore it. When I came back to the UK after diagnosis in 1981, we had to pay for disposable needles and any form of blood testing strips. I had learned their value by getting them free in France.
 
I’m another that often gets a dip in BG soon after going to bed. I think around 3am is often the time when the body’s cortisol output is at its lowest (cortisol raises BG).

I usually try to eat our main meal at around 6pm so that the insulin has mostly been used by the time I go to bed.

Just be prepared for your overnight requirements to carry on changing once you’ve got it ‘perfect’ (just as they do during the day). The Libre is a great tool to help keep track of those pesky changes 😛
 
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