Low blood sugar is a condition that occurs when the body's blood sugar (glucose) decreases and is too low.
Blood sugar below 70 mg/dL is considered low. Blood sugar at or below this level can be harmful.
The medical name of low blood sugar is hypoglycemia.
Insulin is a hormone made by the pancreas. Insulin is needed to move glucose into cells where it is used for energy. Without enough insulin, glucose builds up in the blood instead of going into the cells. This leads to symptoms of diabetes.
Low blood sugar occurs due to any of the following:
- Your body's sugar (glucose) is used up too quickly
- Glucose is released into the bloodstream too slowly
- Too much insulin is released into the bloodstream
Low blood sugar is common in people with diabetes who are taking insulin or other medicines to control their diabetes.
Babies born to mothers with diabetes may have severe drops in blood sugar.
In people who do not have diabetes, low blood sugar may be caused by:
- Drinking alcohol
- Insulinoma, which is a rare tumor in the pancreas that produces too much insulin
- Lack of a hormone, such as cortisol, growth hormone, or thyroid hormone
- Severe heart, kidney, or liver failure
- Infection that affects the whole body
- Some types of weight-loss surgery
Symptoms you may have when your blood sugar gets too low include:
- Double vision or blurry vision
- Fast or pounding heartbeat
- Feeling cranky or acting aggressive
- Feeling nervous
- Shaking or trembling
- Tingling or numbness of the skin
- Tiredness or weakness
- Trouble sleeping
- Unclear thinking
Even if you do not have symptoms, your blood sugar could still be too low. You may not even know you have low blood sugar until you faint, have a seizure, or go into a coma.
Exams and Tests
If you check your blood sugar at home, the reading will be lower than 70 mg/dL on your glucose monitor.
At the hospital, you will likely have blood samples taken from your vein to:
- Measure your blood sugar level
- Diagnose the cause of your low blood sugar
The goal of treatment is to correct your low blood sugar level.
If you have diabetes, it is likely your health care provider told you how to treat yourself for low blood sugar. Treatment can include:
- Drinking juice
- Eating food
- Glucose tablets
Or you may have been told to give yourself a shot of glucagon. This is a medicine that raises blood sugar.
If low blood sugar is caused by an insulinoma (insulin-releasing tumor), surgery to remove the tumor will be recommended.
Severe low blood sugar is a medical emergency. It can cause seizures and brain damage. Severe low blood sugar that causes you to become unconscious is called insulin shock.
Severe low blood sugar may make it less likely for you to have symptoms that allow you to recognize another episode of low blood sugar.
When to Contact a Medical Professional
If signs of low blood sugar do not improve after you have eaten a snack that has sugar:
- Get a ride to the emergency room. DO NOT drive yourself.
- Call a local emergency number (such as 911)
Get medical help right away for a person with diabetes or low blood sugar who:
- Becomes less alert
- Cannot be woken up
Hypoglycemia; Insulin shock; Insulin reaction
American Diabetes Association. Standards of medical care in diabetes -- 20135. Diabetes Care. 2015;38 Suppl 1:S11-S88. PMID 25537706 www.ncbi.nlm.nih.gov/pubmed/25537706.
Cryer PE. Hypoglycemia. In: Melmed S, Polonsky KS, Larsen PR, Kronenberg HM. Williams Textbook of Endocrinology. 12th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 34.
Update Date 10/25/2014
Updated by: Brent Wisse, MD, Associate Professor of Medicine, Division of Metabolism, Endocrinology & Nutrition, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.