You’re seeing roller coaster bg numbers. You know you need to change something, but what? Is it your carb ratio? Your basal? Maybe it’s your ISF? It could even be a mix of two or all three of them! It can be really difficult to know where to start. So, let’s see if we can find the problem.
This post contains affiliate links
I am not a doctor or medical professional. This article is for informational purposes only. If you are thinking about changing the way you treat your diabetes, consult your medical team for assistance.
When you’re seeing roller coaster numbers, it can be easy to just make adjustments and hope for the best. But what if you could test the different aspects of insulin administration so that you know for sure which one (or ones) is the culprit?
In this article, I’m going to go over how to do a carb ratio test.
Your basal has to come first though. When you’re having problems with bg numbers, the first thing you always want to do is a basal test, then, once you know your basal is dialed in correctly, test your carb ratios. If your basal is not set accurately, then doing a carb ratio test is somewhat pointless.
Related: Basal Testing: The Beginner’s Guide
Often, the way basal testing is talked about in the diabetes community, you’d expect your bg numbers to magically get better once you’ve basal tested. And sometimes, that’s the case. But often, it can throw other things out of whack, like your ICR. So, after you’ve done a basal test, it’s always a good idea to follow up with carb ratio testing.
What is a carb ratio?
Let’s back up a bit before we get into how to do a carb ratio test. We should probably talk about what it is that we’re about to test. There are 3 main aspects of insulin dosing when it comes to T1D.
- Basal. Your basal is your background insulin. It is always in your system and is required whether or not you’re eating. Its job is to keep your bg steady in the absence of food, excessive activity, and other insulin.
- Bolus. This is rapid or ultra-rapid-acting insulin that you take when you’re eating. To determine the amount of a bolus, you will use your insulin-to-carb ratio (or ICR). This formula tells you how many units of insulin are required for the food that you’re eating.
- Correction. While a correction might sometimes be part of your bolus, and it can also be referred to as a bolus, it has a slightly different meaning. Corrections are given when your bg is too high, or going too high, whether or not you’re eating food. To figure out how much insulin to give for a correction, you’ll use your insulin sensitivity factor (or ISF). This formula tells you how much insulin to give to get your bg back down in range.
So, to give insulin for food, you need to do a calculation. Your carb ratio helps you calculate how much insulin you need when you eat. You may have different carb ratios for different times of day and your carb ratios are specific to you and your insulin needs.
But, since those insulin needs can change frequently, it’s good to know how to test whether or not they’re working for you.
What is a carb ratio test?
Simply put, it is exactly what it sounds like. You’re setting up a scenario that allows you to test if your current ICR is working properly or not.
You can test all of your various carb ratios in one day if you want. Most people only have 3 or 4 different ratios, usually one for each meal. You simply need to create the right situation for testing starting at breakfast and continuing with your other meals throughout the day.
Ideal conditions:
Before the test:
- You’ve recently basal tested and know that your current basal is accurate. This way basal insulin is not pulling bg up or down, which could mask whether or not your carb ratio is accurate.
- Going into the carb ratio test, your bg is in range and steady. You want it to be in range because you don’t want to complicate things by adding a correction into the mix. Steady is important for the same reason.
- Carb count your food accurately. No SWAGging, guessing, or rounding. You can’t test your carb ratios while using incorrect carb counts.
During the test:
- Don’t eat anything else or give more insulin for 3-4 hours. To see what’s happening with the insulin and food, we need to wait the full insulin duration time before adding new food or insulin to the equation. ** Of course, if you have a low or your bg goes too high, treat it as you normally would. But if this happens, the test didn’t work and needs to be redone.
- Your level of activity during the 3-4 hour test should be average for your daily life. Activity can cause insulin sensitivity and lack of activity can cause insulin resistance. If your activity level is not the norm during your ICR test, then you won’t get an accurate result.
And lastly, to do a carb ratio test, eat whatever is average for your diet. This is important because different foods act differently.
Carb ratios aren’t an exact formula
It’s important to understand that carb ratios are somewhat fluid. Maybe your carb ratio is 1:15, meaning you need one unit of insulin for every 15 grams of carbs. But sometimes, that seems to be too much or too little. There are several reasons for that.
As I already mentioned, activity level can change the way we metabolize insulin and food. It can cause us to become more insulin-sensitive or more insulin resistant. That means, even though your ICR is 1:15 most of the time, you might need to adjust it to 1:12 on a really lazy day or to 1:18 on a very active day.
Similarly, you may need to adjust the ICR for different foods. If your 1:15 carb ratio works well for foods like sandwiches, it may need to be tweaked when you’re eating something very carb-forward like cereal.
What we’re aiming for when testing the carb ratio is a baseline. A ratio that will work well most of the time. So, if you can test at times when your activity level and food intake are typical for your lifestyle, you’ll get the most accurate results.
How to do a carb ratio test
Let’s get to the actual test. It’s pretty simple really. Assuming you’re able to create the ideal conditions listed above, all you have to do is go about your usual day.
If you wake up in the morning and your bg is steady and in range, make sure you accurately carb count your food. Bolus and eat as you usually would using your current ICR. Then, do your best to not eat more or use more insulin until that bolus has worked through your system. Most insulins have a 3-4 hour duration time so you’ll want to wait that long before eating or giving insulin again.
Then, simply monitor your numbers. If you use a CGM, that’s easy. If you do finger pokes, then try to do a few during those 3-4 hours so that you can get a decent idea of what is happening.
Once you’ve gotten that information, you can assess if your ICR is accurate or not.
Basically, there are 4 potential results
There are 4 different ways that your carb ratio test could go. Let’s talk about the different results and what they mean.
1. Your bg went low
The first thing that may happen is your blood glucose drops too low. If this happens, treat it as you would any other low.
The problem with this result is that it doesn’t give us enough information. Many people think that it means the ICR is too strong, and that might be the case. But it could also mean that the ICR is accurate but the pre-bolus timing was too long.
Since we can’t determine which one of those things caused the low (or if it was both of them together) the best option is to try to redo your carb ratio test at a different time.
2. Your bg went up and needed a correction
With this result, it’s important to differentiate between a carb spike and a p/f rise. If the increase in bg started fairly early on, within the first 30-60 minutes, it’s likely the carbs. However, if bg stayed steady for a while and then started to rise after about the 2-hour mark, it’s probably a rise from protein and fat (p/f rise).
It could be that both of these things need to be addressed, but for now, we’ll focus on the carb ratio. Your carb ratio isn’t meant to cover the p/f rise that starts 2-3 hours after eating. If that’s when you saw the rise, the result of your carb ratio test is the 4th scenario on this list and you can move on to learning about how to dose for protein and fat.
Assuming it’s not a p/f rise, here’s what it indicates when bg spikes and stays high until more insulin is given… the carb ratio is not strong enough.
While insulin timing could have played a part in the spike, it’s not the only culprit. If the result of your carb ratio test was this option, you might want to look into adjusting your ICR.
3. Your bg went up and came back down on its own
This is why we have to wait 3-4 hours when doing a carb ratio test. If your bg spiked, but ended up coming back down to roughly the starting number without you adding any more insulin, your ICR is probably fine.
The problem that caused the spike is the food/insulin timing. You might want to recreate the carb ratio test to confirm, but reading up on how to prebolus, glycemic index, and macros might be more beneficial for your T1D management.
4. Your bg stayed fairly steady for the full carb ratio test
Yay!! You nailed it!
This is simple to interpret. Your carb ratio did exactly what it was supposed to do and you timed the bolus and food beautifully. No need to adjust anything with this carb ratio.
If you’ve been seeing erratic numbers lately, which is often why people do carb ratio tests, it might just be that you need to be more intentional about how you calculate your carbs. If you SWAG or guess the carb count frequently, you might be using the wrong carb count in your carb ratio. And that’s going to result in the wrong insulin dose for that food.
That’s it
If your bg is steady enough, you can continue doing ICR tests for lunch and dinner as well. If not, at least you have some information from breakfast and you can set up the other tests on a different day.
It can take a bit of work to figure out what the issue is when our bg numbers are out of whack. But it’s worth doing these tests once in a while. Rather than guessing to make adjustments, you can relax knowing for sure whether or not your ICR is working properly for your T1D management.
Have you ever done a carb ratio test? Did it help you with your T1D management?
For more tips and stories about T1D, join the Carb Counting Mama email list, and make sure to head over to the Carb Counting Mama Facebook page and “like” it.
Leave a Reply