A low glucose result on a blood test means your blood sugar has dropped below the normal range, generally below 70 mg/dL. This condition is called hypoglycemia, and it can range from a mild dip that causes shakiness to a serious drop that leads to confusion or loss of consciousness. Whether the result is something to worry about depends on how low the number is, whether you have symptoms, and what caused it.
What Counts as Low
Blood sugar below 70 mg/dL is considered low. Below 54 mg/dL is considered severely low and requires immediate attention. For context, a normal fasting blood sugar typically falls between 70 and 100 mg/dL.
These thresholds apply whether or not you have diabetes. However, the causes and implications differ. If you take insulin or certain diabetes medications, occasional lows are a known risk of treatment. If you don’t have diabetes and your blood test comes back low, your doctor will likely want to investigate why.
How Low Blood Sugar Feels
The symptoms of low blood sugar fall into two categories, depending on how far your glucose has dropped.
Early symptoms come from your body’s stress response kicking in to signal a problem. These include sweating, shakiness, a racing heart, anxiety, and sudden hunger. Most people notice these first and can act on them.
If blood sugar continues to fall, the brain starts running short on fuel. This produces a different set of symptoms: weakness, dizziness, difficulty concentrating, confusion, blurred vision, and behavior changes that can look like intoxication. In extreme cases, very low blood sugar can cause seizures or loss of consciousness. A reading below 54 mg/dL with altered mental or physical function is classified as a severe episode.
Common Causes in People With Diabetes
For people managing diabetes, low blood sugar most often happens because of a mismatch between medication and food intake. Taking too much insulin, delaying a meal, eating less than usual, or exercising more than expected can all push glucose below 70 mg/dL. Alcohol compounds the problem because it interferes with the liver’s ability to release stored sugar into the bloodstream.
Kidney disease, which is common in long-standing diabetes, can also play a role. The kidneys help clear medications from your body, and when they aren’t working efficiently, diabetes drugs can build up and drive blood sugar lower than intended.
Causes in People Without Diabetes
Low blood sugar in someone who doesn’t have diabetes is less common but has several possible explanations.
- Reactive hypoglycemia: Blood sugar drops within four hours after eating, often after a meal high in refined carbohydrates. The body overproduces insulin in response to the sugar spike, and glucose crashes as a result. The exact mechanism isn’t always clear, but it’s more common after gastric bypass surgery.
- Organ disease: Severe liver illness (such as cirrhosis or hepatitis), advanced kidney disease, and serious heart disease can all impair the body’s ability to regulate glucose.
- Hormonal deficiencies: The adrenal glands and pituitary gland produce hormones that help maintain blood sugar. When these glands underperform, glucose levels can fall.
- Medications: Several non-diabetes drugs can lower blood sugar, including certain beta-blockers, heart rhythm medications, some antibiotics, and certain pain relievers.
- Insulin-producing tumors: Rarely, a small tumor on the pancreas called an insulinoma produces excess insulin. These are uncommon but diagnosable through specialized fasting tests.
- Alcohol: Drinking on an empty stomach can suppress glucose production in the liver, causing a significant drop hours later.
Could the Result Be a Lab Error?
Sometimes a low glucose reading doesn’t reflect what’s actually happening in your body. This is called pseudohypoglycemia, and it’s worth considering if the number doesn’t match how you feel.
The most common cause is delayed processing of the blood sample. After blood is drawn, the cells in the tube continue consuming glucose. If there’s a long gap between the draw and the lab analysis, the reading can come back artificially low. This effect is more pronounced in people with very high white blood cell counts, such as those with leukemia, because more cells means faster glucose consumption in the tube.
Poor circulation can also produce a falsely low reading on a fingerstick test. When blood flow to the fingertips is reduced (from cold hands, low blood pressure, or vascular conditions like Raynaud’s disease), the tissues extract more glucose from the small amount of blood that does reach them, giving a deceptively low number. If your result seems off and you had no symptoms, your doctor may order a repeat test with faster processing to confirm.
What to Do When Blood Sugar Drops
If you check your blood sugar and it’s below 70 mg/dL, the standard approach is called the 15-15 rule: eat or drink 15 grams of fast-acting carbohydrates, wait 15 minutes, then recheck. If it’s still below 70, repeat the process until your level returns to your target range. Good sources of 15 grams of carbs include four glucose tablets, half a cup of juice or regular soda, or a tablespoon of honey.
Avoid overcompensating with a large meal, which can send blood sugar soaring in the other direction. Once your level stabilizes, follow up with a balanced snack or meal that includes some protein and fat to keep it steady.
For severe episodes where someone is confused, unable to swallow safely, or unconscious, the situation is a medical emergency. People on insulin are sometimes prescribed an emergency glucagon kit for exactly this scenario.
What Happens After an Unexpected Low Result
If a low glucose level shows up on routine bloodwork and you don’t have diabetes, your doctor will typically want to confirm the finding and look for a cause. The diagnostic process usually involves checking whether the low reading occurs alongside symptoms and whether both the symptoms and the low reading resolve once blood sugar is brought back up. This three-part pattern (low reading, symptoms, and resolution with glucose) is the classic framework doctors use to confirm true hypoglycemia.
From there, the workup depends on the pattern. If your blood sugar drops after meals, the focus is on reactive hypoglycemia and dietary triggers. If it drops during fasting, the investigation turns toward hormone levels, liver and kidney function, and occasionally imaging to rule out an insulin-producing tumor. Blood tests measuring insulin and a related marker called C-peptide, drawn during an episode of low blood sugar, help distinguish between the body overproducing insulin and other causes.
A single mildly low reading on a blood test, especially one without symptoms, isn’t always cause for alarm. But repeated lows or a reading well below 70 mg/dL warrants a closer look to make sure nothing is being missed.