If you are using CGM (Continuous Glucose Monitor), you already know how many game-changers this technology can make when it comes to diabetes management.
Getting insight into our history of blood sugar, what our blood sugar is for now, where it is, and where it is, brings peace of mind, making managing diabetes much easier, Safer.
But even if you love your CGM, do you use trending arrows for insulin adjustments? If not, you are truly missing out on the possibilities of technology completely.
Paying attention to the arrows in CGM trends allows for more aggressive and informed choices regarding insulin dose adjustments.
The information in this post is specific to the Dexcom CGM system. Other CGM systems also use trend arrows, but please note that if you are using other systems, we will utilize the information here.
Open the Dexcom app or look at the receiver and you will see that you will see your current blood sugar level and what will happen in 30 minutes.
The signs come in the form of arrows. On the receiver, the arrow is on the right side of your current blood glucose level. The app shows it as a circle with arrows around the blood sugar level and circle.
You probably know that the arrow above indicates that your blood sugar levels are rising and that it shows a down arrow that is falling, but do you know how much and how to include it in your insulin adjustment?
According to the manufacturer, start with what the arrows indicate.
| Trend Arrows | meaning |
| Raise the two arrows straight up | BG can exceed 90 mg/dL (5 mmol/L) in 30 minutes. |
| Straighten one arrow | BG can increase up to 90 mg/dL (5 mmol/L) in 30 minutes. |
| One arrow is a little above | BG can increase 30-60 mg/dL (1.7-3.3 mmol/L) in 30 minutes. |
| One arrow next to it | There is no increase or decrease in BG above 1 mg/dL (0.05 mmol/L) per minute. |
| 1The arrow is slightly lowered | BG can reduce 30-60 mg/dL (1.7-3.3 mmol/L) in 30 minutes. |
| One arrow straight down | BG can decrease to up to 90 mg/dL (5 mmol/L) in 30 minutes. |
| The two arrows are straight down | BG can exceed 90 mg/dL (5 mmol/L) in 30 minutes. |
sauce: Dexcom G6 Guide
Real life examples
Let’s say my blood sugar level is 120 mg/dL (6.7 mmol/L) and Dexcom shows two arrows straight up.
In this case, we can expect blood glucose levels to exceed 210 mg/dL (120 + 90) within the next 30 minutes.
I try to stay below 200 mg/dl, so I’m most likely giving myself a correction bolus based on this knowledge (as long as I have not eaten a meal and I have enough active insulin that’s not yet on board).
Arrows in CGMS can be very helpful in managing your blood sugar levels, but only if you know how to respond to those arrows.
Several health professionals have come up with an approach to help patients administer insulin safely and effectively using CGM arrows. Most importantly, they all agree that rising or falling rates should be taken into consideration when adjusting insulin doses. But what they disagree is to make sure that you are precisely how to adjust your insulin dose based on those arrows.
The Endocrine Society reviewed four published approaches in 2017 and came up with its own guidelines. Their guidelines have been published in Journal of the Endocrine Society December 2017 (Note that the guidelines explained here are adults only).
I consider the Endocrine Society to be the highest authority when it comes to this type of recommendation, so I intend to share their recommendations with you.
The guidelines are written for the Dexcom G5, but no changes have been made to the arrows on the new system, and the recommendations must also be in effect on the Dexcom G6.
The Endocrine Society recommends adjusting insulin based on blood glucose levels in 30 minutes, not the current one. However, instead of calculating future blood glucose levels in 30 minutes, it is recommended to adjust the correction factor (CF).
This correction should be made on top of corrections for current blood sugar levels and carbohydrates consumed.
Your CF is how much a unit of rapidly acting insulin (such as Humanlog or Novolog) reduces your blood sugar level. If you are using a pump, you can check the CF in the settings. If you manage your diabetes with injections and don’t know about CF, you can ask your medical team to help with your calculations.
Endocrine Society recommendation revision based on Dexcom trend arrows
| An arrow appears | Correction coefficient (CF) | Corrected Dose (IU) |
| Raise the two arrows straight up | <25 25-50 50-75 > 75 |
+4.5 +3.5 +2.5 +1.5 |
| Straighten one arrow | <25 25-50 50-75 > 75 |
+3.5 +2.5 +1.5 +1 |
| One arrow is a little above | <25 25-50 50-75 > 75 |
+2.5 +1.5 +1 +0.5 |
| One arrow next to it | <25 25-50 50-75 > 75 |
No adjustment No adjustment No adjustment No adjustment |
| 1The arrow is slightly lowered | <25 25-50 50-75 > 75 |
-2.5 -1.5 -1- 0.5 |
| One arrow straight down | <25 25-50 50-75 > 75 |
-3.5 -2.5 -1.5 -1 |
| The two arrows are straight down | <25 25-50 50-75 > 75 |
-4.5 -3.5 -2.5 -1.5 |
sauce: https://academic.oup.com/jes/article/1/12/1445/4642923
Let’s summarize with an example:
I’m out of bed in the morning and trying to sit for a 20 gram carb meal as I wasn’t low overnight. My blood sugar level is 120 mg/dL (6.8 mmol/L) and two arrows rise. This means that you need to do three calculations:
- First, you need to calculate the carbohydrate dose. Assuming my insulin-to-carbohydrate ratio (ICR) is 10, I need 2 IU of insulin to cover 20 grams of carbohydrate.
- Second, you need to calculate the corrective dose based on your current blood glucose. If my CF is 25 and my target blood glucose is 95 mg/dL (5.3 mmol/L), my corrected dose is 1 IU (120-95 = 25 and 25/25 = 1 IU).
- Third, you need to calculate the correction based on the arrows. There are two arrows according to the recommendation and the CF is 25, so a 3.5 IU fix is required.
Adding all my total doses gives me 2 iu + 1 iu + 3.5 iu = 6.5 iu.
If I had seen my blood sugar level lower than my target, or I was looking at the downward arrow, I would have finished with a lower recommended dose.
To make sure that makes sense, let’s give another example.
I’m rolling out of bed again and trying to sit down for a 20 gram carb diet, and now my blood sugar level is 120 mg/dL (6.8 mmol/L).
What has been changed compared to the last example is the direction of the arrow that changes calculation #3.
I now have one arrow straight down and my CF is 25. According to recommendations, a -2.5 IU fix is required.
Adding it all makes my new total dose 2 iu + 1 iu – 2.5 iu = 0.5 iu
Fau, that’s a lot of mathematics. See the next section of how I simplify it.
The endocrine recommendation makes perfect sense to me, but it’s a lot of mathematics! You also cannot take less than 0.5 IU with correction (which can be a problem if you are very sensitive to insulin).
I would rather use a bolus calculator than do all the maths every time I need it for a bolus for a meal or a modified dose. If you have a pump, it is likely that there is a built-in bolus calculator. If you’re doing multiple daily injections (MDIs) like me, you need to see elsewhere.
In the past, I used an app called RapidCalc for these calculations. I’m currently using Inpen, a SmartPen that has an associated app that sends data directly to my phone via Bluetooth, calculates the dose and tracks the IOB.
The Inpen app and RapidCalc basically do the same thing as a bolus calc, but give me my dose actually (Please note that the RapidCalc app is not FDA approved).
After completing the basic calculations in Bolus Calculator, you can manually add trend arrow corrections based on CF.
Don’t forget to respond based on what you’re doing in the next 1-4 hours, not what you’re doing when you’re about to do a bolus.
If you are planning on exercising or planning more travel than usual (such as walking, shopping, cleaning, gardening), you may not need to respond as aggressively as the guidelines do.
In general, it is recommended to reduce the bolus before exercise and potentially reduce the basal (if using a pump). Regular rapid insulin is active in the body for up to 4 hours (some people may see the tail up to 6 hours after injection), so it should be thought before the bolus.
There are new, super-acting insulins available now, and endocrine guidelines do not work for these. If you are using Afrezza or FIASP, know that these insulins peak much faster and applying the above calculations can be very dangerous.
If you do not use CGM trend arrows
All publications advocating for using trending arrows to make insulin adjustments state that there are situations where you should never use them, or at least take strict precautions.
If you plan to start adjusting your insulin dose using trendy rows, read these precautions first.
4-hour meal window
The Endocrine Society recommends that the trend arrows not be used four hours after eating on a bolus. Instead, they recommend:
- 2 hours after meal – Do not fix hyperglycemia to prevent insulin stacking
- Blood glucose level 150-250 mg/dl (8.3-13.9 mmol/l) with one or two arrows raised for 2-4 hours after meal – Consider using CF to adjust
- 2-4 hours after meal > 250 mg/dl (13.9 mmol/l) with one or two arrows raised – Check with your fingertips and fix using ketone test (>300 mg/dl/16.7 mmol/l), injection.
- Blood glucose level near 150 mg/dl (8.3 mmol/l) with one arrow slightly below, 2-4 hours after measurement – Check again in 30 minutes
- Lower one or two arrows 2-4 hours after blood glucose near 150 mg/dl (8.3 mmol/l) – Check again in 15 minutes
- 2-4 hours after blood glucose near 100 mg/dl (5.6 mmol/l), one arrow is slightly below, or one arrow is below – Consider eating 15 g of carbohydrates and rechecking in 20 minutes. > For 70 mg/dl (3.9 mmol/l) and downward arrows, check with your fingertips and consider a faster carb of 15 g
- 2-4 hours of meal, blood sugar near 100 mg/dl (5.6 mmol/l) – Follow the instructions above (f) to eat 30 g of carbohydrates
Blood sugar levels rise rapidly
If you see two arrows on the receiver or app before meals, it is best to be enthusiastic about pre-bolus and inject 15-20 minutes of insulin before eating.
Blood sugar levels drop rapidly
If you have two down to the receiver or app before a meal, do not inject it when starting a meal or if it is close to 150 mg/dl (8.3 mmol/l) until BGS is leveled.
Fragile / Elderly
For vulnerable or older adults, the Endocrine Society recommends less aggressive insulin dose adjustments to limit the risk of hypoglycemia.
The rising arrows recommend a 50% reduction in the recommended adjustment (1 IU to 0.5 IU to 0.5 IU), while the downward arrow recommends a 50% reduction (for example, 1 IU to 2 IU).
Illness Day Management and Medication Considerations
Certain medications, both prescription and OTC, can interfere with CGM readings, and as a result, do not use trend arrows to adjust insulin. Instead of relying entirely on CGM, attach a finger bar to your CGM measurements.
Always use common sense before administering
Like all tools in the Diabetes Toolkit, we recommend not applying recommendations blindly.
If you feel that the recommended dose can be turned off, it can depend on how well you know your body is the path.
Dexcom G5 and G6 CGMs are approved for administration by the FDA, but sometimes they can be inaccurate, so always check them with your fingertips before making large-scale dosing adjustments.
