The Best Time to Check Blood Sugar

Living with diabetes includes monitoring your blood sugar (also called blood glucose) levels. Most people do this by pricking their fingers with a blood sugar meter (glucometer), which measures sugar in a small amount of blood.

Some people use a continuous glucose monitor (CGM), a sensor under the skin that checks blood sugar every few minutes. People who use a CGM must also use a blood sugar meter daily to ensure their CGM is accurate.

When you have diabetes, monitoring blood sugar levels is crucial because keeping blood sugar in a target range can help prevent complications, including:

• Heart disease
• Kidney disease
• Vision problems

When you check your blood sugar matters. There are several times throughout the day that health experts recommend checking your blood sugar.

This article explains the importance of monitoring your blood sugar, how blood sugar is measured, and how to check it.

Why Check Blood Sugar?

Whether you have type 1 diabetes or type 2 diabetes, checking your blood sugar lets you see what makes your blood sugar go up or down. For example, some factors that can make blood sugar rise are:

• Too much food, especially carbohydrates
• Inactivity
• Lack of insulin (a hormone that metabolizes food)
• Certain medications
• Illness
• Stress
• Pain
• Menstruation
• Dehydration

In addition, the following factors may result in low blood sugar levels:

• Insufficient food consumption
• Alcohol
• Too much insulin
• Some medications
• More physical activity than usual

Understanding your body’s patterns can help you and your healthcare provider know how to manage your diabetes best. For example, monitoring your blood sugar levels and keeping your blood sugar within your target range reduce the risk of diabetes complications.

In addition, managing your diabetes can help prevent severely high blood sugar (hyperglycemia) and severely low blood sugar (hypoglycemia).

How Is Blood Sugar Measured?

Blood sugar levels are measured differently depending on which device you use.

Blood Sugar Monitor

Blood sugar meters work by using a piece of paper coated in an enzyme (glucose oxidase) that reacts with glucose in the blood. In addition, there is an electrode in the meter that creates an electrical signal when it detects the glucose reaction.

This signal then generates a number that correlates to the electrical signal. The more glucose in the blood, the higher the number.

Continuous Glucose Monitor (CGM)

You wear continuous glucose monitors (CGMs) under the skin on your belly or arm. Rather than measuring the glucose levels in blood, like the blood sugar meter, the CGM measures glucose levels in the fluid between your cells. The sensor then sends the information to a monitor.

When to Check Blood Sugar

How often you check your blood sugar may depend on several factors, including:

• The type of diabetes you have
• If you take insulin (a manufactured version of the hormone made by the pancreas) or other medication to manage your diabetes

Type 1 Diabetes

People with type 1 diabetes (also called "juvenile diabetes" because it appears in childhood) need to check their blood sugar frequently. Blood sugar monitoring for type 1 diabetes is centered around mealtimes and includes:

• Before breakfast, lunch, and dinner
• Two to three hours after each meal

Type 2 Diabetes

People with type 2 diabetes who manage their diabetes with insulin must check their blood sugar levels regularly. Again, always work with your healthcare provider to determine the correct frequency for your circumstance. However, general guidelines suggest checking blood sugar four times a day at the following intervals:

• When you first wake up (fasting)
• Before a meal
• Two hours after a meal
• At bedtime

People with type 2 diabetes whose condition is well controlled may not need to monitor their blood sugar as frequently.

Medication Type

There are many different types of drugs that work to lower blood sugar. The type of drug you take may influence how frequently your healthcare provider recommends you test your blood sugar levels.

For example, if you take insulin or medication that can cause hypoglycemia, your doctor will likely recommend more frequent blood sugar monitoring.

Target Range

Target ranges for blood glucose levels are personalized and based on many factors, including:

• How long you have had diabetes
• Your age
• Other health conditions or complications

The American Diabetes Association recommends the following target ranges for most adults with diabetes who are not pregnant:

• Preprandial plasma glucose (your glucose level before eating a meal): 80–130 milligrams per deciliter (mg/dL)
• Postprandial plasma glucose (your glucose level one to two hours after starting a meal): less than 180 mg/dL

In addition to measuring your blood sugar levels at home, your healthcare provider will periodically order blood tests to monitor your blood sugar levels. The A1C measures your average blood sugar levels over the past two or three months. This level should be less than 7%. An alternate way of reporting A1C is eAG. In this case, it should be less than 154 mg/dL.

How to Test Blood Sugar

People with diabetes usually check their blood sugar levels themselves. However, it’s a good idea to have a roommate, friend, or family member also know how to do it if you are sick and can’t do it yourself. 

To use a blood sugar meter, follow these steps:

1. Wash your hands.
2. Insert a test strip into the meter.
3. Obtain a drop of blood by pricking the side of your fingertip with the device.
4. Place the edge of the test strip to the blood and await the results to appear on the display.

If you are interested in CGM, you should talk to your healthcare provider since these are prescription devices. To use CGM, follow these steps:

1. Place the sensor under the skin on your belly or arm.
2. Most CGM devices check glucose levels every five minutes, around the clock. You don’t need to do anything for this to occur.
3. View the information that the sensor transmits. This data may go to a separate receiver, your cellphone, or an insulin pump.
4. Download the data to a computer to share with your healthcare provider (some CGM devices do this automatically).

You will also need to change the sensors on the CGM regularly, usually every one to two weeks. 

Summary

Monitoring blood sugar levels is essential for people living with diabetes because keeping blood sugar within a target range can help prevent complications from the disease. People often do this with a blood sugar monitor, which involves pricking your finger so the machine can measure the sugar levels in your blood.

People with well-controlled type 2 diabetes may not need to check blood sugar levels very often. However, those with type 1 diabetes and those who use medication or insulin to manage their diabetes will need to check their blood sugar frequently, often before and after every meal.

A Word From Verywell

If you have diabetes, you may be wondering when you should check your blood sugar levels. Since there are many types of diabetes and levels of severity, you will need to work closely with your healthcare provider to develop a plan that is best for your situation. If you are worried about checking frequently or have difficulty using a blood glucose monitor, you may want to talk to your healthcare provider about CGM.