Guidelines for when to test blood sugar

It's essential for people with type 1 diabetes (t1d) to know when to test blood sugar, either with fingersticks or by monitoring blood sugar with a continuous blood glucose monitor (CGM). Determining and keeping track of your blood glucose levels is vital to effective diabetes management.

According to the Mayo Clinic, your doctor may recommend gauging your blood glucose levels four to 10 times a day if you have t1d. Here's a helpful guide for when it's best to test blood sugar.

Right when you wake up

Testing blood sugar when you wake up will indicate if you need to change your normal insulin and carbohydrate intake on a particular day. In addition, if you discover a pattern of highs or lows when you wake up, it will help determine whether you should change your normal daily regimen.

Before meals and snacks

Determining blood sugar levels before meals and snacks will help you to make adjustments in your meals or insulin dosage. For example, when my blood glucose is too high, my doctor and I have worked out a plan for how much extra short-acting (bolus) insulin to take based on certain blood sugar levels.

Before and after exercise

The American Diabetes Association notes that testing blood sugar before you exercise is important. Since physical activity can cause low blood sugar, you might need to adjust your insulin dosage or carbohydrate intake before exercising. Consult with your doctor about the adjustments that might be necessary before you work out.

On the other hand, if your blood sugar is too high, it can actually increase during physical activity. This happens when the body releases stress hormones that raise glucose levels while you exercise, according to the Cleveland Clinic.

In the same article, endocrinologist Betul Hatipoiglu advises that if you test your blood sugar and find that the glucose level is 300 mg/dL or more, postpone exercise for a bit and try taking a little insulin before starting to work out. Again, discuss how to handle that situation with your healthcare provider.

Testing or monitoring after you finish your workout is also important. Low blood sugar can occur long after physical activity if you've been exercising strenuously or for an extended period of time.

When you're sick

When you're ill, glucose levels can go up even if you're eating less than you usually do.

The Joslin Clinic recommends testing your blood sugar 4 times per day during mild illnesses (like a cold) or every three to four hours for more severe illnesses (like the flu). Determining your glucose levels more often when you are ill is crucial because increases can happen quickly. You won't always know if your blood sugar is high based on how you're feeling — especially if you're already under the weather.

When taking certain medications

There are medications that can cause low blood sugar. These include beta blockers for arrhythmia and other heart problems, certain drugs that fight pain and infection, and other medications listed here by MedlinePlus of the U.S. National Library of Medicine. If you're prescribed these medications, discuss when to test your blood sugar with your doctor.

Before going to sleep

Almost half of all low blood sugar episodes occur at night during sleep, according to a report by Johns Hopkins. Testing your blood sugar before bed can help reduce the chance of low blood sugar during sleep by letting you know whether you need to manage your blood sugar beforehand.

Sometimes...in the middle of the night

Low blood sugar episodes can happen while you're sleeping, even to people who carefully manage their diabetes, including t1d veterans like me. When I relied on fingersticks and wasn't absolutely confident about my blood glucose levels, I used to set my alarm clock and do blood tests in the middle of the night. That's one of the reasons why having a CGM is so helpful. It automatically beeps and wakes me up when my blood glucose swoops down to a certain level, which tells me to eat foods containing glucose.

Keep a record to track trends

For optimal management of t1d, you should keep track of trends in your blood glucose levels in order to determine if adjustments are needed in insulin dosage or diet. Ideally, that means keeping a record of when you eat and the amount of carbs for each meal or snack, when and how much insulin you take, and whether you've exercised.

The easiest way to do this is with CGM technology that allows you to easily enter this information into a smartphone or a computer. Another alternative is to write the information down in a journal. Sometimes, I use both. When there are special circumstances that affect my blood sugar-like stressful situations or illness, I try to jot them down and share them with my doctor.

Interested in learning more about when to test blood sugar? Check out this article on factors that affect blood glucose levels.