Monitoring Blood Sugar With Diabetes: What To Know

If your healthcare provider has recommended that you check your blood sugar at home, you probably have several questions – when should you monitor it, and what should you do with that information?

In this article, we’ll explore the several ways monitoring your blood sugar can benefit you, as well as tips on when to check your glucose.

What are normal blood sugar levels?

When it comes to “normal blood sugar” levels, there are two sets of normal: one for people without diabetes and one for people with diabetes.

In people without diabetes, normal blood sugar levels are as follows:

  • Fasting blood sugar (at least eight hours without food or drink besides water): below 100 mg/dL
  • Postprandial blood sugar (within two hours of starting a meal): below 140 mg/dL

For people with diabetes, these are generally considered normal blood sugar levels:

  • Fasting: between 80-130 mg/dL
  • Within two hours of starting a meal: <180 mg/dL

Blood sugar targets for gestational diabetes are a bit more strict due to the risks high blood sugar has for both the mother and unborn baby. 

Blood sugar targets for GDM are:

  • Fasting: <95 mg/dL
  • One hour after eating: <140 mg/dL
  • Two hours after eating: <120 mg/dL

If your blood sugar levels fall outside of these ranges over a long period, it can cause damage to your blood vessels and lead to diabetes complications such as kidney disease, vision problems (retinopathy), heart disease, and more.

Diagnosing diabetes with blood sugar levels

You might be wondering at what level your blood sugar needs to be diagnosed with diabetes or prediabetes. 

Prediabetes and diabetes are usually diagnosed with a fasting blood sugar level, a hemoglobin A1c test, or both.

The hemoglobin A1c test is generally preferred because it measures your average blood sugar over the past 2-3 months.

PrediabetesDiabetesNormal (no diabetes)
Fasting blood sugar100-125 mg/dL>126 mg/dL<100 mg/dL
Hemoglobin A1c5.7-6.4%6.5%+<5.6%

Why should you test your blood sugar?

There are several benefits to checking your blood sugar levels. Let’s look at a few of the best reasons to monitor your blood sugar at home, not just at your regular diabetes check-ups.

Without checking your blood sugar regularly, you’re less likely to be aware of the times when your blood sugar is high. 

While you can have symptoms when your blood sugar levels are very high, you generally can’t feel high blood sugar levels.

If your body is used to high blood sugar levels, then you’re even less likely to have any symptoms when it’s high.

Some people might not be aware when their blood sugar is low or trending down. For instance, if your blood sugar is 100 mg/dL at bedtime and you don’t check it, injecting a bedtime dose of insulin could drop it too low while you sleep.

Know when to check for ketones

Diabetic ketoacidosis (DKA) is a serious condition that mostly impacts people with type 1 diabetes. 

When your blood sugar levels are very high, your body can go into ketosis due to the lack of insulin available. 

If you check your blood sugar and it’s very high, you’ll know to check for ketones to see if you need to seek medical attention for DKA.

Prevent and treat hypoglycemia

Hypoglycemia is the term for low blood sugar. The definition of hypoglycemia is when blood sugar falls below 70 mg/dL. 

Low blood sugar comes with several common symptoms, but not all people are aware of when they’re experiencing a low. 

Hypoglycemia unawareness is a condition when you can no longer tell when you’re experiencing low blood sugar. 

Fortunately, this condition can improve as you prevent future bouts of low blood sugar, and your body’s responses can become more sensitive to it.

Checking your blood sugar when you feel symptoms helps you better treat hypoglycemia. If you monitor your blood sugar and it’s low, you’ll need to treat it by eating or drinking 15 grams of carbohydrates and re-checking your blood sugar in 15 minutes, repeating the process until your blood sugar is above 70 mg/dL.

Without checking your blood sugar, you wouldn’t know how it was responding to the treatment or if you needed to seek medical attention for a severe bout of hypoglycemia (below 54 mg/dL).

Adjust insulin doses

If you’re taking insulin to manage your diabetes, you might need to adjust your dose based on your blood sugar readings. 

This is especially true if you’re taking mealtime insulin on a “sliding scale,” which is when you adjust your insulin dose based on your blood sugar before you eat.

Here is an example of a sliding scale insulin regimen for mealtimes:

  • Blood sugar level 180 or higher: inject 6 units of insulin
  • Blood sugar level 150 mg/dL or higher: inject 4 units of insulin
  • A blood sugar level of 120 mg/dL or higher: inject 2 units of insulin
  • Blood sugar <120 mg/dL: no insulin

As you can see, you wouldn’t be able to accurately follow a sliding scale without checking your blood sugar at mealtimes!

Calibrate insulin pump therapy

If you’re using an insulin pump, you’ll need to monitor your blood sugar level often to make sure your insulin settings are promoting blood sugar levels within your goal range.

Some people choose to use a continuous glucose monitor (CGM) with their insulin pump, but if you don’t have a CGM, you’ll need to check your blood sugar with a standard glucometer. 

If you have an insulin pump, you’ll likely need to check your blood sugar at least four times daily, if not more.

Help make lifestyle changes to reach your blood sugar targets

Another benefit of checking your blood sugar is that it can help you identify things you can change about your lifestyle habits to promote good blood sugar control. 

For instance, if you monitor your blood sugar after your largest meal of the day and keep a log of what you eat, you can better identify the types of meals that raise your blood sugar too much and those that are better for your blood sugar.

Checking your blood sugar on a day that you’ve exercised might also give you the motivation to keep exercising once you see how much it can help to lower your blood sugar.

You can experiment with different types of exercise to see which lowers your blood sugar the most.

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When to test your blood sugar

Your healthcare provider will likely offer guidance on how often they’d like you to monitor your blood sugar at home. 

They might even specify how often when (and if) they write a prescription for blood glucose test strips, which will influence how often you can go in for refills.

In general, these are some of the best times to check your blood sugar.

When to testHow to use the information
Morning/fastingGet an idea of your baseline blood sugar before you eat anything/while you’re fasting.
Adjust basal insulin dose.
Before mealsAdjust mealtime insulin dose accordinglyAssess the change in blood sugar before and after a meal.
Within 2 hours of eatingAssess how effective mealtime insulin dose is and make adjustments as needed.
Track how your meals are impacting your blood sugar.
BedtimeAdjust basal insulin dose as needed, especially if you’re taking long-acting insulin morning and night.
Assess changes in blood sugar from bedtime to the next morning.
When you’re experiencing symptoms of low blood sugarEffectively identify and treat low blood sugarSeek emergency medical care as needed.
Adjust insulin dose as needed to reduce the prevalence of hypoglycemia.

How to monitor blood sugar

To monitor your blood sugar, you’ll need a glucometer kit, which usually contains most of these elements:

  • A glucometer
  • Test strips
  • A lancing device to prick your finger
  • Carrying case for your glucometer supplies
  • A blood sugar log or app

Be sure to check your blood sugar when your hands are clean, and always dispose of the needles in a biohazard container. 

Follow the instructions in the manual of your blood sugar monitor and record the readings in a log or an app, being sure to specify the time you checked. 

For even more helpful information, try to keep a record of your meals, medication schedule (such as insulin dosages), and activity so you can get a better picture of what is impacting your blood sugar.

Keeping track of your other medications is helpful as there are some medications that can raise your blood sugar level.

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Types of glucose monitors

There are several different brands of glucometers to choose from, but they’ll all fall under two basic categories:

Continuous glucose monitors measure your blood sugar every few minutes all day long.

Standard glucose monitors are the most popular type. 

These monitors give you a blood sugar reading when you obtain a blood sample and insert it into a test strip, giving you a one-time reading.

Which glucometer you end up with will likely depend on your healthcare coverage, any coupons offered by the manufacturer to make it more affordable, your personal preferences, and your diabetes history (what type you have, how often you experience hypoglycemia, etc). 


Checking your blood sugar gives you more insight into your blood sugar trends and can help prevent very high and very low blood sugar levels.

The two types of blood glucose monitors (glucometers) are standard and continuous; the latter is primarily for use among patients with type 1 diabetes but can also be used by people with type 2 diabetes and even prediabetes.

Keeping a log of your blood sugar levels, in addition to information about your medications, diet, and exercise, can help you and your healthcare provider make more informed decisions about your diabetes care.

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