- 01Low reading vs low disorder
For people on insulin or sulfonylureas, any reading under 70 mg/dL is a low to treat; for everyone else, a low disorder is diagnosed only when symptoms, a low reading at that moment and relief after sugar all line up.
Low blood sugar, or hypoglycemia, is blood glucose below 70 mg/dL (3.9 mmol/L). The American Diabetes Association uses that line as the alert level, calls anything under 54 mg/dL (3.0 mmol/L) clinically significant, and calls any low that needs another person's help severe, whatever the meter says 1. Real lows mostly happen to people on insulin or sulfonylurea pills (diabetes tablets such as glipizide that make the pancreas release more insulin). When people who get shaky a few hours after meals test during the spell, most readings are normal 4.
The marker behind this page
What counts as low blood sugar
The ADA grades hypoglycemia in three levels, built for people with diabetes who check their glucose 1. To convert, divide mg/dL by 18 to get mmol/L.
| Level | mg/dL | mmol/L | What it means |
|---|---|---|---|
| Normal fasting | 70 to 99 | 3.9 to 5.5 | Where most fasting results sit 7 |
| Level 1 | 54 to 69 | 3.0 to 3.8 | Alert value: treat it and recheck |
| Level 2 | Under 54 | Under 3.0 | Clinically significant; brain symptoms become likely |
| Level 3 | Any number | Any number | Severe: confusion or collapse that needs someone else's help |
CalculatorGlucose converterYour meter or lab report in mmol/L? Convert any glucose number both ways.Work it out People without diabetes are judged differently. Healthy people, especially women, children and anyone on a long fast, can read below 70 mg/dL with no symptoms and no disease, so the Endocrine Society says a number alone does not diagnose a low outside diabetes 2. In people without diabetes, symptoms usually start around 53 mg/dL 3.
For people with diabetes who wear a continuous glucose monitor (CGM), the international consensus target is less than 4% of the day below 70 mg/dL (about one hour) and less than 1% below 54 mg/dL (about 15 minutes) 5.
Where a fasting glucose of 62 sits (example)mg/dL
Low blood sugar symptoms
Symptoms come in two families. The first set comes from adrenaline, the body's alarm, and usually shows up first. The second set appears when the brain itself is short of glucose, which is called neuroglycopenia, and it is the dangerous one 2.
| Warning signs (adrenaline) | Brain short of fuel |
|---|---|
| Shaking, trembling | Confusion, trouble concentrating |
| Sweating, clammy skin | Blurred or double vision |
| Racing or pounding heart | Slurred speech, clumsiness |
| Sudden hunger | Odd behavior, irritability |
| Anxiety, feeling on edge | Drowsiness |
| Tingling lips or tongue | Seizure or passing out |
Lows during sleep show up differently: nightmares, waking with damp sheets or night sweats, and a headache or hungover feeling in the morning. Related symptom guides cover <a href="/symptoms/dizziness">dizziness</a>, <a href="/symptoms/heart-palpitations">heart palpitations</a>, <a href="/symptoms/night-sweats">night sweats</a> and <a href="/symptoms/brain-fog">brain fog</a>.
Hypoglycemia unawareness is when the adrenaline warnings fade, usually after repeated lows, so the first sign is confusion. Strictly avoiding lows for several weeks, with your diabetes care team adjusting treatment, can bring some of the warning symptoms back 1.
What to do right now: the 15-15 rule
For a conscious person who can swallow, the ADA advises 15 to 20 g of glucose, a recheck about 15 minutes later, and another round if glucose is still low 1. Pure glucose works fastest; any sugar that contains glucose works too 1. No meter to hand? Treat anyway.
- 1Take 15 g of fast sugarFour glucose tablets, half a cup (4 oz) of juice or regular soda, or 1 tablespoon of sugar or honey. Chocolate, cookies and other fatty foods raise glucose more slowly 1.
- 2Wait 15 minutesSit down and stop driving, exercising or operating anything. Glucose needs time to absorb.
- 3RecheckStill under 70 mg/dL (3.9 mmol/L)? Repeat the 15 g and check again in 15 minutes. If it is still low after two or three rounds, or the person is getting more confused or drowsy, call 911.
- 4Eat once you are back upOnce your glucose is back above 70 mg/dL, have your next meal or a snack to keep it from dropping again 1. This matters most when a long-acting medicine caused the low.
Lows caused by sulfonylureas such as glyburide or glipizide can come back for many hours. After one, call your prescriber the same day, and get urgent care if the low keeps returning 2.
Why blood sugar drops: causes with and without diabetes
Insulin and the pills that push the pancreas to release insulin (sulfonylureas such as glipizide and glyburide, and meglitinides) cause most lows. Metformin, GLP-1 drugs, SGLT2 inhibitors and DPP-4 inhibitors rarely cause a low on their own, though they can add to the effect of insulin or a sulfonylurea 1. People without diabetes have a shorter, rarer list 2.
| Cause | Who it affects | Clue |
|---|---|---|
| Insulin or sulfonylurea | People with <a href="/conditions/type-2-diabetes">type 2</a> or type 1 diabetes | Dose and meal out of step, extra exercise, or a skipped meal |
| Alcohol | Anyone, worse on an empty stomach | Low hours after drinking, often overnight; the liver stops releasing glucose |
| Severe illness | Kidney failure, liver failure, sepsis, starvation | Already unwell; the low is one sign among many |
| <a href="/biomarkers/cortisol-am">Low cortisol</a> (adrenal insufficiency) | Rare; also after stopping long-term steroids | <a href="/symptoms/fatigue">Fatigue</a>, weight loss, low blood pressure, salt craving |
| After gastric bypass | Months to years after surgery | Lows a few hours after meals |
| Insulinoma | Very rare, about 4 per million people a year | A small, usually harmless tumor of the pancreas that makes insulin; lows while fasting or after exercise |
| Someone else's diabetes pills | Rare, sometimes a pharmacy mix-up | Lows without diabetes; a sulfonylurea drug screen finds it |
Source for the causes without diabetes, including the insulinoma rate and lows after gastric bypass: Cryer 2009 2.
Reactive hypoglycemia: the crash 2 to 4 hours after eating
Reactive hypoglycemia is the name people give to feeling shaky, hungry or foggy a few hours after a meal, often a meal heavy in sugar or refined carbs. When people with this complaint wore meters and tested during their episodes in a 1989 NEJM study, the readings were rarely in the low range 4. Glucose does dip after a fast rise, but in most people the dip stays above 70 mg/dL, and the symptoms come from the speed of the fall and the adrenaline response to it.
The real, measurable version exists after gastric bypass, where lows after meals are a recognized complication that needs a specialist 2. Post-meal swings are also common in <a href="/conditions/insulin-resistance">insulin resistance</a> and <a href="/conditions/prediabetes">prediabetes</a>. Smaller mixed meals with protein, fat and fiber, fewer sugary drinks and refined carbs, and alcohol only with food may help flatten the post-meal curve for many people; a doctor or dietitian can tailor this to you.
Shaky but your blood sugar is normal?
Low-sugar symptoms at a normal reading have three common explanations.
- A shifted threshold. In Boyle's 1988 NEJM study, people with poorly controlled diabetes felt low at about 78 mg/dL, while people without diabetes felt low at about 53 mg/dL 3. When glucose usually runs high, a normal number can feel like a low until the body adjusts. Doctors call this relative hypoglycemia.
- The meter. Cold fingers, a sugary fingertip or an old strip all skew a finger-stick, and a CGM lags blood by several minutes and can read falsely low when you sleep lying on the sensor. A falsely low reading with no true low is called pseudohypoglycemia.
- A different condition with the same symptoms, as in the table below.
| Mimic | What sets it apart | What gets checked |
|---|---|---|
| Anxiety or panic | Comes on with stress, any time of day, normal glucose during the spell | Glucose during symptoms |
| <a href="/conditions/hyperthyroidism">Overactive thyroid</a> | Constant tremor, weight loss, heat intolerance | <a href="/biomarkers/tsh">TSH</a> |
| <a href="/conditions/anemia">Anemia</a> | Tired and breathless on exertion, pale | <a href="/biomarkers/hemoglobin">Hemoglobin</a>, <a href="/biomarkers/ferritin">ferritin</a> |
| Low cortisol | <a href="/symptoms/fatigue">Fatigue</a>, weight loss, dizziness on standing | <a href="/biomarkers/cortisol-am">Morning cortisol</a> |
| Too much caffeine | Shaky within an hour of coffee or energy drinks | No specific test; mention your caffeine intake to your doctor |
A low fasting glucose on your blood test
The most common reason for a low fasting glucose on a routine panel, such as 60 to 69 mg/dL, is the tube itself. Red and white blood cells keep burning glucose after the draw, and in a sample left unprocessed at room temperature glucose falls by roughly 5 to 7% an hour 6. A sample that sat for three hours before spinning can turn a true 80 into a reported result in the mid-to-high 60s. A very high white cell count speeds this up.
Lean, active people and anyone who fasted longer than usual can also read in the 60s with no disease 2. With no symptoms and no diabetes medicine, a single reading in the 60s is usually repeated, ideally with prompt processing; the clinician who ordered it can arrange that. A result under 54 mg/dL, a low with symptoms, or a low in someone on diabetes medicine is a reason to call a doctor. The <a href="/biomarkers/glucose-fasting">fasting glucose guide</a> covers the full range.
How a doctor confirms a true low
Outside diabetes, the Endocrine Society recommends looking for a cause only when Whipple's triad is documented 2:
...symptoms, signs, or both consistent with hypoglycemia, a low plasma glucose concentration, and resolution of those symptoms or signs after the plasma glucose concentration is raised.
The key step is blood drawn during a low, either one that happens on its own or one brought on safely under medical supervision (a fast of up to 72 hours, or a test meal for post-meal symptoms). The lab checks glucose plus the hormones that show what caused the drop: insulin, C-peptide, proinsulin, a ketone called beta-hydroxybutyrate (low when insulin is driving the drop) and a screen for diabetes pills 2.
Glucose under 55 mg/dL with insulin of at least 3 microU/mL, C-peptide of at least 0.6 ng/mL and proinsulin of at least 5 pmol/L means the body is making too much of its own insulin, as with an insulinoma 2. The standard <a href="/biomarkers/ogtt-2h-glucose">oral glucose tolerance test</a> is not used, because healthy people often dip low on it. A1C and fasting glucose give background on average levels; see <a href="/compare/a1c-vs-fasting-glucose">A1C vs fasting glucose</a> and <a href="/learn/blood-sugar-explained">blood sugar explained</a>.
Tests taken during a low
Preventing lows
- On insulin or a sulfonylurea: eat regular meals, carry fast sugar, and check glucose before driving and before exercise.
- Drink alcohol with food, and check before bed after drinking, because alcohol lows can come overnight.
- Tell your prescriber about repeated lows or lows at night; the dose or the drug may need to change, and only the prescriber should change it.
- Some supplements also lower glucose. <a href="/compounds/berberine">Berberine</a> and <a href="/compounds/chromium">chromium</a> can add to diabetes medicine, so mention them to your prescriber; <a href="/compare/berberine-vs-metformin">berberine vs metformin</a> compares the evidence.
When to get help
See a doctor soon for a confirmed low under 70 mg/dL in someone who takes no diabetes medicine, repeated lows on treatment, lows at night, new lows after weight-loss surgery, or a lab result under 54 mg/dL.
This page is general education, not medical advice, and does not diagnose or replace care from your own clinician; talk to them about what your results mean for you. If someone is confused, having a seizure, has passed out or cannot swallow safely, do not put food or drink in their mouth: use glucagon if it is available and call 911. If you take insulin or a sulfonylurea and have repeated lows, talk to your prescriber before changing any dose.
Citations
- ADA Professional Practice Committee. 6. Glycemic goals, hypoglycemia, and hyperglycemic crises: Standards of Care in Diabetes 2026. Diabetes Care 2026;49(Suppl 1).
- Cryer PE et al. Evaluation and management of adult hypoglycemic disorders: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab 2009;94(3):709-728.
- Boyle PJ et al. Plasma glucose concentrations at the onset of hypoglycemic symptoms in patients with poorly controlled diabetes and in nondiabetics. N Engl J Med 1988;318:1487-1492.
- Palardy J et al. Blood glucose measurements during symptomatic episodes in patients with suspected postprandial hypoglycemia. N Engl J Med 1989;321:1421-1425.
- Battelino T et al. Clinical targets for continuous glucose monitoring data interpretation: recommendations from the international consensus on time in range. Diabetes Care 2019;42(8):1593-1603.
- Sacks DB et al. Guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus. Diabetes Care 2023;46(10):e151-e199.
- ADA Professional Practice Committee. 2. Diagnosis and classification of diabetes: Standards of Care in Diabetes 2026. Diabetes Care 2026;49(Suppl 1).
Educational context only, not medical advice or a diagnosis. Always discuss your results with a clinician.
