What blood sugar level is dangerous?
Under 70 mg/dL (3.9 mmol/L) with shakiness or sweating needs 15 g of fast sugar now, like half a cup of juice, and under 54 (3.0) is serious. Confusion, fainting or trouble swallowing means call 911. On the high side, blood sugar that stays at 300 or more, or comes with vomiting, fruity breath or hard breathing, means the ER or 911.
What we’d do
Learn the two numbers that need action today, 70 on the low side and 300 on the high side, and the symptoms that turn either one into a 911 call. If you take insulin or a sulfonylurea, keep fast sugar with you and make sure the people around you know what a low looks like.
If you remember three things
- Under 70 with symptoms means fast sugar. Have 15 g, check again in 15 minutes, and repeat if you’re still under 70.
- Confused, fainting or unable to swallow means 911. Don’t put food or drink in the mouth of someone who can’t swallow.
- Staying at 300 or more means the ER. Vomiting, fruity breath or hard breathing with high blood sugar do too. Go now or call 911.
Why people worry about the wrong number
It’s easy to worry about a 160 after dinner or a 105 in the morning. Those are reasons to book a lab test. The numbers that are dangerous right now are the very low ones and the very high ones that don’t come down, and they come with symptoms you can feel.
The lows
The sugar in your blood is critical fuel for many of your cells, and there’s only about 4 grams of it in the whole bloodstream of an adult, so a drop shows up fast. The CDC lists shaking, sweating, a fast heartbeat, nervousness, irritability or confusion, dizziness and hunger. As it gets worse, people feel weak, have trouble walking or seeing, act strangely, or have seizures. Below 54 they may faint.
| Level | mg/dL | mmol/L | What to do |
|---|---|---|---|
| Low (level 1) | under 70 | under 3.9 | 15 g of fast sugar, check again in 15 minutes |
| Serious (level 2) | under 54 | under 3.0 | the same, and the 15-15 rule may not be enough. Glucagon if you have it |
| Severe | any low with confusion, fainting or needing help | any | call 911 |
Fifteen grams is 4 ounces (half a cup) of juice or regular soda, 3 to 4 glucose tablets, or a tablespoon of sugar, honey or syrup (CDC). The first two levels come from the international consensus on sensor targets in diabetes, and the severe level from the American Diabetes Association.
Lows are mostly a side effect of diabetes treatment. The Endocrine Society names insulin and the pills that make the pancreas release more insulin, such as sulfonylureas, as the most common cause. Severe lows can happen in people not on insulin too (American Diabetes Association).
A sensor is a different story. Healthy people spent about 15 minutes a day under 70 on a blinded sensor. A low number on your arm with no symptoms isn’t an emergency, so check it with a finger stick.
The highs
Very high blood sugar that doesn’t come down can turn into diabetic ketoacidosis, where the body runs short of insulin and starts making acids called ketones. It usually builds slowly, starting with strong thirst and peeing a lot. The CDC says to go to the ER or call 911 if:
- your blood sugar stays at 300 mg/dL (16.7 mmol/L) or above
- your breath smells fruity
- you’re vomiting and can’t keep food or drinks down
- you’re having trouble breathing
A blood sugar of 200 or more with strong thirst, peeing a lot, blurry vision or weight loss you didn’t try for means calling your doctor today.
It’s like a car’s warning lights. Most lights mean book a service, and a few mean pull over now.
The full list of when to book a test, call today or call 911 is on when to see a doctor. If you feel shaky after meals, see why do I feel shaky a few hours after eating?
9 sources
- CDC, Treat low blood sugar (hypoglycemia)cdc.gov
- CDC, Low blood sugar (hypoglycemia)cdc.gov
- American Diabetes Association, Severe hypoglycemiadiabetes.org
- American Diabetes Association, Hypoglycemia (low blood glucose)diabetes.org
- Battelino T and others, Clinical targets for continuous glucose monitoring data interpretation: recommendations from the International Consensus on Time in Range, Diabetes Care, 2019pmc.ncbi.nlm.nih.gov
- CDC, Diabetic ketoacidosiscdc.gov
- Cryer PE and others, Evaluation and management of adult hypoglycemic disorders: an Endocrine Society clinical practice guideline, Journal of Clinical Endocrinology and Metabolism, 2009pubmed.ncbi.nlm.nih.gov
- Shah VN and others, Continuous glucose monitoring profiles in healthy nondiabetic participants: a multicenter prospective study, Journal of Clinical Endocrinology and Metabolism, 2019pmc.ncbi.nlm.nih.gov
- Wasserman DH, Four grams of glucose, American Journal of Physiology, Endocrinology and Metabolism, 2009pmc.ncbi.nlm.nih.gov
