Throughout the day, depending on multiple factors, blood glucose (also called blood sugar) levels will vary—up or down. This is normal. If it varies within a certain range, you probably won’t be able to tell. But if it goes below the healthy range and is not treated, it can get dangerous.

Low blood glucose is when your blood glucose levels have fallen low enough that you need to take action to bring them back to your target range. This is usually when your blood glucose is less than 70 mg/dL. However, talk to your diabetes care team about your own blood glucose targets, and what level is too low for you.

Low blood glucose may also be referred to as an insulin reaction, or insulin shock.

Signs and symptoms of low blood glucose (happen quickly)

Each person's reaction to low blood glucose is different. Learn your own signs and symptoms of when your blood glucose is low. Taking time to write these symptoms down may help you learn your own symptoms of when your blood glucose is low. From milder, more common indicators to most severe, signs and symptoms of low blood glucose include:

• Feeling shaky
• Being nervous or anxious
• Sweating, chills and clamminess
• Irritability or impatience
• Confusion
• Fast heartbeat
• Feeling lightheaded or dizzy
• Hunger
• Nausea
• Color draining from the skin (pallor)
• Feeling sleepy
• Feeling weak or having no energy
• Blurred/impaired vision
• Tingling or numbness in the lips, tongue, or cheeks
• Headaches
• Coordination problems, clumsiness
• Nightmares or crying out during sleep
• Seizures

The only sure way to know whether you are experiencing low blood glucose is to check your blood glucose levels, if possible. If you are experiencing symptoms and you are unable to check your blood glucose for any reason, treat the hypoglycemia.

A low blood glucose level triggers the release of epinephrine (adrenaline), the “fight-or-flight” hormone. Epinephrine is what can cause the symptoms of hypoglycemia such as thumping heart, sweating, tingling, and anxiety.

If the blood sugar glucose continues to drop, the brain does not get enough glucose and stops functioning as it should. This can lead to blurred vision, difficulty concentrating, confused thinking, slurred speech, numbness, and drowsiness. If blood glucose stays low for too long, starving the brain of glucose, it may lead to seizures, coma, and very rarely death.

Treatment—The "15-15 Rule"

The 15-15 rule—have 15 grams of carbohydrate to raise your blood glucose and check it after 15 minutes. If it’s still below 70 mg/dL, have another serving.

Repeat these steps until your blood glucose is at least 70 mg/dL. Once your blood glucose is back to normal, eat a meal or snack to make sure it doesn’t lower again.

This may be:

• Glucose tablets (see instructions)
• Gel tube (see instructions)
• 4 ounces (1/2 cup) of juice or regular soda (not diet)
• 1 tablespoon of sugar, honey, or corn syrup
• Hard candies, jellybeans, or gumdrops—see food label for how many to consume

Make a note about any episodes of low blood glucose and talk with your health care team about why it happened. They can suggest ways to avoid low blood glucose in the future.

Many people tend to want to eat as much as they can until they feel better. This can cause blood glucose levels to shoot way up. Using the step-wise approach of the "15-15 Rule" can help you avoid this, preventing high blood glucose levels.

Note:

• Young children usually need less than 15 grams of carbs to fix a low blood glucose level: Infants may need 6 grams, toddlers may need 8 grams, and small children may need 10 grams. This needs to be individualized for the patient, so discuss the amount needed with your diabetes team.
   
• When treating a low, the choice of carbohydrate source is important. Complex carbohydrates, or foods that contain fats along with carbs (like chocolate) can slow the absorption of glucose and should not be used to treat an emergency low.

Severe hypoglycemia

When low blood glucose isn’t treated and you need someone to help you recover, it is considered a severe event.

Treating severe hypoglycemia

Glucagon is a hormone produced in the pancreas that stimulates your liver to release stored glucose into your bloodstream when your blood glucose levels are too low. Glucagon is used to treat someone with diabetes when their blood glucose is too low to treat using the 15-15 rule.

Glucagon is available by prescription and is either injected or administered or puffed into the nostril. For those who are familiar with injectable glucagon, there are now two injectable glucagon products on the market—one that comes in a kit and one that is pre-mixed and ready to use. Speak with your doctor about whether you should buy a glucagon product, and how and when to use it.

The people you are in frequent contact with (for example, friends, family members, and coworkers) should be instructed on how to give you glucagon to treat severe hypoglycemia. If you have needed glucagon, let your doctor know so you can discuss ways to prevent severe hypoglycemia in the future.

Steps for treating a person with symptoms keeping them from being able to treat themselves.

1. If the glucagon is injectable, inject it into the buttock, arm, or thigh, following the instructions in the kit. If your glucagon is inhalable, follow the instructions on the package to administer it into the nostril.
2. When the person regains consciousness (usually in 5–15 minutes), they may experience nausea and vomiting.

Don’t hesitate to call 911. If someone is unconscious and glucagon is not available or someone does not know how to use it, call 911 immediately.

Do NOT:

• Inject insulin (it will lower the person's blood glucose even more)
• Provide food or fluids (they can choke)

Causes of low blood glucose

Low blood glucose is common for people with type 1 diabetes and can occur in people with type 2 diabetes taking insulin or certain medications. The average person with type 1 diabetes may experience up to two episodes of mild low blood glucose each week, and that’s only counting episodes with symptoms. If you add in lows without symptoms and the ones that happen overnight, the number would likely be higher.

Insulin

Too much insulin is a definite cause of low blood glucose. One reason newer insulins are preferred over NPH and regular insulin is that they’re less likely to cause blood glucose lows, particularly overnight. Insulin pumps may also reduce the risk for low blood glucose. Accidentally injecting the wrong insulin type, too much insulin, or injecting directly into the muscle (instead of just under the skin), can cause low blood glucose.

Food

What you eat can cause low blood glucose, including:

• Not enough carbohydrates.
• Eating foods with less carbohydrate than usual without reducing the amount of insulin taken.
• Timing of insulin based on whether your carbs are from liquids versus solids can affect blood glucose levels. Liquids are absorbed much faster than solids, so timing the insulin dose to the absorption of glucose from foods can be tricky.
• The composition of the meal—how much fat, protein, and fiber are present—can also affect the absorption of carbohydrates.

Physical activity

Exercise has many benefits. The tricky thing for people with type 1 diabetes is that it can lower blood glucose in both the short and long-term. Nearly half of children in a type 1 diabetes study who exercised an hour during the day experienced a low blood glucose reaction overnight. The intensity, duration, and timing of exercise can all affect the risk for going low. 

Medical IDs

Many people with diabetes, particularly those who use insulin, should have a medical ID with them at all times.

In the event of a severe hypoglycemic episode, a car accident or other emergency, the medical ID can provide critical information about the person's health status, such as the fact that they have diabetes, whether or not they use insulin, whether they have any allergies, etc. Emergency medical personnel are trained to look for a medical ID when they are caring for someone who can't speak for themselves.

Medical IDs are usually worn as a bracelet or a necklace. Traditional IDs are etched with basic, key health information about the person, and some IDs now include compact USB drives that can carry a person's full medical record for use in an emergency.

Hypoglycemia unawareness

Very often, hypoglycemia symptoms occur when blood glucose levels fall below 70 mg/dL. As unpleasant as they may be, the symptoms of low blood glucose are useful. These symptoms tell you that you your blood glucose is low and you need to take action to bring it back into a safe range. But, many people have blood glucose readings below this level and feel no symptoms. This is called hypoglycemia unawareness.

People with hypoglycemia unawareness can't tell when their blood glucose gets low so they don’t know they need to treat it. Hypoglycemia unawareness puts the person at increased risk for severe low blood glucose reactions (when they need someone to help them recover). People with hypoglycemia unawareness are also less likely to be awakened from sleep when hypoglycemia occurs at night. People with hypoglycemia unawareness need to take extra care to check blood glucose frequently. This is especially important prior to and during critical tasks such as driving. A continuous glucose monitor (CGM) can sound an alarm when blood glucose levels are low or start to fall. This can be a big help for people with hypoglycemia unawareness.

Hypoglycemia unawareness occurs more frequently in those who:

• Frequently have low blood glucose episodes (which can cause you to stop sensing the early warning signs of hypoglycemia).
• Have had diabetes for a long time.
• Tightly manage their diabetes (which increases your chances of having low blood glucose reactions).

If you think you have hypoglycemia unawareness, speak with your health care provider. Your health care provider may adjust/raise your blood glucose targets to avoid further hypoglycemia and risk of future episodes.

Regaining hypoglycemia awareness

It’s possible to get your early warning symptoms back by avoiding any, even mild, hypoglycemia for several weeks. This helps your body re-learn how to react to low blood glucose levels. This may mean increasing your target blood glucose level (a new target that needs to be worked out with your diabetes care team). It may even result in a higher A1C level, but regaining the ability to feel symptoms of lows is worth the temporary rise in blood glucose levels.

Other causes of symptoms

Other people may start to have symptoms of hypoglycemia when their blood glucose levels are higher than 70 mg/dL. This can happen when your blood glucose levels are very high and start to go down quickly. If this is happening, discuss treatment with your diabetes care team.

How can I prevent low blood glucose?

Your best bet is to practice good diabetes management and learn to detect hypoglycemia so you can treat it early—before it gets worse.

Monitoring blood glucose, with either a meter or a CGM, is the tried and true method for preventing hypoglycemia. Studies consistently show that the more a person checks blood glucose, the lower his or her risk of hypoglycemia. This is because you can see when blood glucose levels are dropping and can treat it before it gets too low.

If you can, check often!  

• Check before and after meals.
• Check before and after exercise (or during, if it’s a long or intense session).
• Check before bed.
• After intense exercise, also check in the middle of the night.
• Check more if things around you change such as, a new insulin routine, a different work schedule, an increase in physical activity, or travel across time zones.

Why am I having lows?

If you are experiencing low blood glucose and you’re not sure why, bring a record of blood glucose, insulin, exercise, and food data to a health care provider. Together, you can review all your data to figure out the cause of the lows. 

The more information you can give your health care provider, the better they can work with you to understand what's causing the lows. Your provider may be able to help prevent low blood glucose by adjusting the timing of insulin dosing, exercise, and meals or snacks. Changing insulin doses or the types of food you eat may also do the trick.

If you're new to type 2 diabetes, join our free Living With Type 2 Diabetes program to get help and support during your first year.