Blood glucose, or blood sugar, is the primary source of energy for every cell in your body, particularly the brain. Glucose comes directly from the food you eat and is transported through the bloodstream to fuel bodily functions. Maintaining a stable blood glucose concentration is a tightly regulated process performed by hormones like insulin, which moves glucose into cells, and glucagon, which releases stored glucose when levels drop. This regulatory balance is important because both excessively high and dangerously low blood sugar levels can quickly lead to acute health crises. When blood sugar deviates too far from this target, the body enters a “danger zone” where immediate action is required to prevent serious complications.
Establishing the Baseline
The non-dangerous ranges for blood sugar provide context for understanding the danger zones. For a healthy individual without diabetes, a normal fasting blood glucose level, measured after at least eight hours without food, falls between 72 and 99 milligrams per deciliter (mg/dL). Before a meal, this level is usually in the range of 70 to 90 mg/dL.
After eating, blood sugar naturally rises as carbohydrates are digested and absorbed, but the body quickly works to bring it back down. Two hours after a meal, a non-diabetic level should be below 140 mg/dL. For individuals managing diabetes, target ranges are often slightly higher and vary based on age, duration of diabetes, and other health conditions.
Generally, a common target for people with diabetes is a pre-meal level between 80 and 130 mg/dL, with a two-hour post-meal level less than 180 mg/dL. These ranges serve as the healthy corridor, and significant deviations below 70 mg/dL or persistently above 250 mg/dL signal entry into a danger zone that requires attention.
The Low Danger Zone Hypoglycemia
The low danger zone is defined by hypoglycemia, which begins when blood glucose drops below the threshold of 70 mg/dL. At this level, the body’s counter-regulatory hormones begin to kick in, causing physical symptoms as the brain starts to be deprived of its main energy source.
Initial physical symptoms often include a fast heartbeat, shakiness, sweating, and nervousness or anxiety. These are alarm signals triggered by adrenaline, which attempts to stimulate the release of stored glucose. As the glucose level continues to fall, below 55 mg/dL, cognitive and neurological symptoms appear.
The brain’s function becomes impaired, leading to confusion, irritability, difficulty concentrating, slurred speech, and blurred vision. When blood sugar drops to severely low levels, below 50 mg/dL, the immediate risk increases to seizures, loss of consciousness, and potentially coma. Severe hypoglycemia is a medical emergency because the lack of fuel can lead to irreversible neurological damage if not corrected quickly.
The High Danger Zone Hyperglycemia
The high danger zone, known as hyperglycemia, involves blood sugar levels that are acutely or persistently elevated, typically above 180 mg/dL after a meal. While a single reading above this level may not be an immediate crisis, a level consistently over 250 mg/dL signals a serious problem that requires action. Immediate symptoms of this moderate high range include increased thirst, frequent urination, and fatigue, as the body attempts to flush excess sugar through the kidneys.
When blood sugar rises to very high levels, often above 300 to 400 mg/dL, the risk of acute, life-threatening complications becomes significant. In individuals with type 1 diabetes or severe insulin deficiency, sustained elevation leads to the body breaking down fat for energy, producing acidic byproducts called ketones. This results in a rapid buildup of acid in the blood, causing severe symptoms like nausea, vomiting, abdominal pain, and rapid, deep breathing.
A second acute risk, more common in type 2 diabetes, involves extreme dehydration caused by the kidneys eliminating massive amounts of glucose, which pulls water from the body. This state presents with severe dehydration, confusion, and sometimes difficulty staying awake. In both scenarios, the body is in a profound state of metabolic crisis that requires emergency medical intervention.
Emergency Response Actions
When blood sugar falls below 70 mg/dL, the immediate response is to follow the “Rule of 15” for mild to moderate hypoglycemia. This involves consuming 15 grams of a fast-acting carbohydrate, such as four ounces of fruit juice, a half-can of regular soda, or glucose tablets. After waiting 15 minutes, the blood sugar should be rechecked; if the level is still below 70 mg/dL, the 15-gram treatment is repeated until the number is back in the safe range.
For severe hypoglycemia, defined as a level below 55 mg/dL or when the person is unable to safely swallow, immediate medical help is needed. In these cases, a glucagon injection or nasal spray is the treatment of choice, as this hormone rapidly stimulates the liver to release stored glucose. Anyone experiencing severe confusion, seizures, or loss of consciousness requires emergency services immediately.
For high blood sugar, treatment involves administering insulin or other prescribed medications, increasing fluid intake, and checking for ketones. Emergency medical attention is necessary if high blood sugar is accompanied by vomiting, persistent nausea, severe abdominal pain, or any change in mental status. These symptoms indicate a severe metabolic crisis requiring professional medical care.