Dexcom Clarity CGM data - opinion?

Hi All, I just started using Dexcom CGM 2 weeks ago and since then, has been shocked by the spike I experience after every breakfast, lunch and dinner. I tried a few modification with bolusing but nothing seems to help, my BG reading 1-2 hours after meal always shoot over 200mg/dL.

Please see the attached pattern, do you all experience so much fluctuations as I do? Is 200mg/dL postmeal going to do me much harm in the long run? I am worried as I never knew my BG spikes so high in the past 16 years of my T1D life.

Sorry, I couldn’t access the file but your words paint a clear enough picture. I can’t say for sure but you do have an insulin/food mismatch going on. Likely a combo of weak basal and a timid insulin to carb ratio. Timing also plays a pivotal role. How much time did you prebolus?

Thank you for your opinion. My endo and CDE were previously worried about my frequent lows, that’s why they set my basal low at 0.2u/hr. After exercise I usually reduce that to 0.15u/hr for 16 hours. I always bolus and eat right away. Recently I started hearing some people pre-bolus so I tried pre-bolusing 20 minutes before breakfast of oatmeal+cereal+milk of about 32g carb. But that doesn’t seem to prevent a post meal spike above 200mg/dL. Do I have to pre-bolus much earlier?

please try again to upload your file, sometimes it doesn’t take.

One of the most dangerous things (that I still struggle with myself, btw) of having a CGM/meter is looking at your 1-hour after eating number. Short-acting insulin hangs around for as long as 6 hours. If you have the right basal and have bolused correctly, it is important to look at your BG (and make conclusions) much later.

I would start to individualize your treatment protocol based on what the CGM is telling you. Each of us is going to have a slightly different response. Here’s how I might approach the data.

Pre-Bolus - does your CGM start trending down when you bolus @ 20 minutes before your meal? What about @ ‘X’ other time before? I find that I have to vary my pre-bolus time based on my pre-meal BG level. If I am in range and above 80 mg/dl, 15 minutes is the max for me. If I am between 70 - 80, an absolute maximum of 5 minutes is all I need.

Post Prandial - What does your BG look like @ 3-4 hours after eating? Is it trending down and/or approaching your BG level before the meal? Remember your bolus may still be acting up to 6 hours afterwards. I eat higher carb than many here @ TuD, and I often have a rise of 70 - 100 points, but 4 hours later I’m back in range. Bottom line here is that IMO I wouldn’t get too concerned over a +200 spike IF you are coming back into range after digesting the meal, AND your basal is keeping you in range. OTOH, if you are running +200 and staying there for 3+ hours, then you have a problem

Basal - How are those basal rates working out for you? Have you tried reducing your basal rate 1 hour BEFORE exercise? My gut reaction without seeing your trending data is that 16 hours is a L-O-N-G time.

That may simply just be more carbohydrates than your body can process in one meal, especially first thing in the morning. Or it may be the source of the carbohydrate.

There was a thread on oatmeal, and a lot of people said they don’t eat it because it spikes them too much. If you are drinking low-fat/skim milk, especially, you are getting a lot of carbs with only a very little protein and next to no fat to slow down the carb absorption.

Depending on what kind of meals you are eating, it may simply be a matter of timing. Hopefully you can get the chart loaded. It may be easier to post it somewhere else and link it here.

You may also need a better insulin-to-carb ratio, but one that doesn’t leave you going low at the 3 or 4 hour mark. Hopefully with your Dexcom information, and a detailed food log that list what you ate, your doctor can help you sort it out.

since you have a CGM , sugar surfing is relatively* easy.

I’m a big fan of “doing the experiment.” With your CGM, it’s easy to watch your blood sugar level after dosing and wait for the downward bend in the glucose trace. Stephen Ponder, author of Sugar Surfing, calls this “waiting for the bend.”

Employing this tactic, I found that I often have to wait up to 60 minutes in the morning after dosing and before I eat. It would be best to do this at home on a day without other pressing commitments. Have your meal ready to go on short notice. It’s not the same 60-minute pre-bolus time for me every day but it usually ends up in the 30-60 minute range.

The reason that I like personal experimentation with my diabetes is that I can discover my body’s unique metabolism, not some stock general answer. Your CGM is a wonderful asset in treating your diabetes. Watching it closely will reveal all kinds of useful information to you.

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I concur completely on personal experimentation, because if I wake up in a range from about 95 - 80 mg/dl bolus for my morning meal and “wait for the bend”, I will run low. I find myself setting a 15 minute timer and eating when it goes off. The only time I don’t follow this routine is if my CGM shows an upward bend @ 15 minutes.

I’ve witnessed the same thing. If my morning glucose when I dose is in the 75-90 mg/dl range, I will often eat 15-30 minutes later and show good post meal BGs.


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The above is my BG pattern after uploading to Dexcom Clarity. Please share your opinion, I really appreciate everyone’s comment and advice!

You are doing a good job keeping your BGs in a relatively tight range. In other words, the width of your 14-day trace is not too fat.

You have a strong pattern of lows, 2x/day, followed by highs. Solve the lows and you’ll find the highs will tend to fall back in range, too. If this were my report I would start with going after the hypos. I think your overnight hypos are leading to morning and afternoon rebound highs.

You will need to think about why these lows are happening. The easy answer is that you have too much insulin or not enough food or exercise that drives the BGs lower. I think you are very close to producing a much less variable BG with a a high percentage of your time in range.

Is it your habit to take high BG corrections in the evening hours leading up to bedtime? If that’s the case then you should look at your dinner dosing amount and timing. If you are correcting the highs with insulin, you might consider giving less insulin to correct.

Since this is a strong pattern, I would not hesitate to set an alarm for 1:30 a.m. to check your BG and treat if necessary. Make an extra effort not to over-treat a low if you have one. The 15/15 rule (eat 15 grams of carbs and wait 15 minutes to check again) does not work well for most people. I will often correct a low BG by taking 1 glucose tab, 4 grams of carbs. If I have a unit or two of insulin on board (IOB) then I may take a second glucose tab.

If you are not taking insulin corrections in the evening hours before bed, then you need to consider your basal profile. You may need to back off on the basal rate starting at 11:30 p.m. at least through 5:00 a.m. The key here is making the basal rate change two hours before you wish to see an effect.

Your late afternoon, around 4:30 p.m., lows are a classic time when a lot of us tend to go hypo. I would reduce your basal rate starting at 2:30 p.m. I like to make my basal rate changes in 0.1 unit steps but this amount needs to be adjusted based on your usual basal rate. My rates vary from 0.4 to 1.2 units per hours, so a 0.1 unit change is a reasonable step. If your rates were much less, like 0.1 to 0.5 units per hour, you may consider basal step changes of 0.05/hour.

Good luck. I think you’re doing a better job than you might give yourself credit for and you’re not that far away from much better performance.


Thanks for the insight. They are really helpful!

Pre-bolus - I just started trying out pre-bolus for a few times, and from what I see, it takes at least 20-30 minutes for the CGM to show the downward bend. So maybe that’s when I should start eating.

Post Prandial - My BG usually spike highest at 1hour postmeal, after which it will decrease. By 3-4 hours after meal, it is usually around 100-160mg/dL, depending on the time of the day. Perhaps I am only overly concerned about the 1 hour spike, as I have read some articles that says even a short period of spike above 200mg/dL can lead to diabetic complications in the long term. Even more concerned because I have had diabetes for 17 years and didn’t notice that all these years, my BG had been going up above 200mg/dL at 1 hour after every meal. This thought cause me huge anxiety.

Basal - I suspect my current basal at 0.2u/hr may be a little too low. I should probably use 0.25-0.3u/hr. The reason is because I tend to see a gradual increase between meals when the IOB from previous meal has run out. As for the 16 hours’ reduced basal, it seems to be fine so far.

I have to agree with Terry. Deal with the lows first; once you have those handled you might try doing some proper basal testing you might try skipping breakfast and seeing what happens to your trend. You can try this with your different meal times. But I would space it out a few days apart to give your body a break in between. If you are slowing drifting up I would think you might need a touch more basal. I would do this on a day that you can stay around the house. You could even just try sleeping late.

I find that my insulin resistance rates are much higher in the morning and so depending on my fasting sugar I have to ramp up the bolus accordingly; if I am in the higher part of my range.

Keep in mind also that our post meal sugars use to be a bit of a joke years ago. I remember doctors tell me don’t waste your blood strips on after meal tests. But the technology was just not what it is today. I remember back in the early 90s seeing sugars in the 230-260s after 1 hour. Do the best you can with the data you have now. Keep in mind you can’t fix yesterday. But you can certainly learn and adapt; I am always trying to re-invent the way I do things to take better care of myself. Sometimes my experiments work great and things fall into place. Other times things go wrong and I just chock it up to the randomness of our disease.

Good luck to you.

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Thank you! So far I have not done any BG corrections, because I want to track the effect of the boluses on my BG spikes after meals. You are right, I should probably wake up at 1.30am to check my BG to avoid midnight lows.

Oh! It is relieving to hear I am not the only one experiencing low in late afternoon. I think reducing basal at late afternoon is a good idea!

Good idea. I never had actually done a proper basal testing, or even work out my ICC ratio with accurate carb counting. I go my estimates all this while because where I came from in Asia, diabetes education is not well established. I am grateful now I have support from good endos, CDE and you all in the diabetes community who generously share your wisdom and experiences. I am absorbing like a dry sponge! :grinning:

Thank you!

Indeed! I am drinking low fat milk. That explains the fast absorption.
I just read the oatmeal thread, and am sad as oatmeal is one of my favorite food and main source of fibre. Guess I just have to find other source of fibre if nothing works out.

What is bolusing?

A bolus is a dose of insulin taken to cover a meal or to bring down a high blood glucose. It can be delivered by a pump, pen, or syringe. This contrasts with basal insulin that is delivered as a drip over time in a pump or as a long acting insulin like Lantus, Levemir, or Tresiba.