Blood glucose, or blood sugar, is the primary energy source for the body’s cells, especially the brain and muscles. Glucose comes directly from consumed food and is regulated by the hormone insulin. The body must maintain sugar within a narrow range because both too much and too little rapidly affect cellular function. When glucose levels fall outside this optimal range, the body enters a state of imbalance that can quickly become a serious health threat.
Understanding Target Blood Sugar Levels
For people without diabetes, blood sugar levels are maintained in a consistent range by automatic processes. A normal fasting glucose reading, taken after not eating for at least eight hours, is generally below 100 milligrams per deciliter (mg/dL). Two hours after a meal, levels usually peak at no more than 140 mg/dL before returning to the fasting range.
Individuals managing diabetes work with their healthcare providers to establish a personalized target range that is considered well-controlled. The American Diabetes Association suggests a goal of 80–130 mg/dL before a meal for many adults. The post-meal target is typically set at under 180 mg/dL two hours after eating. These target numbers serve as a baseline, providing a clear reference point to measure when levels are approaching a dangerous imbalance.
The Danger Zone of Low Blood Sugar
The danger zone for low blood sugar, known as hypoglycemia, begins when the glucose concentration drops below 70 mg/dL. At this threshold, the body releases counter-regulatory hormones, such as adrenaline, to raise blood sugar. This hormonal surge causes the initial symptoms of hypoglycemia, including shakiness, sweating, and a rapid heart rate.
As the blood sugar level continues to fall, the brain begins to be starved of its fuel source, leading to neuroglycopenic symptoms. These symptoms can progress from difficulty concentrating and confusion to slurred speech and poor coordination. If the level drops further, typically below 54 mg/dL, it is considered severe hypoglycemia and can rapidly lead to seizures, loss of consciousness, or coma. This profound drop can happen quickly, which is why immediate recognition and response are important.
The progression of symptoms is a warning sign that the central nervous system is malfunctioning due to lack of energy. This is a medical emergency because the brain requires a constant supply of glucose to function correctly. Without prompt treatment, severe hypoglycemia can result in permanent neurological damage or death.
The Danger Zone of High Blood Sugar
The danger zone for high blood sugar, or hyperglycemia, involves two distinct, severe acute complications. While high levels are generally defined as above 180 mg/dL, the acute danger threshold is often considered to be sustained levels above 250 mg/dL. The two primary acute threats are Diabetic Ketoacidosis (DKA) and Hyperosmolar Hyperglycemic State (HHS).
Diabetic Ketoacidosis (DKA) commonly affects people with Type 1 diabetes when there is a severe lack of insulin. Without insulin, the body breaks down fat for energy, producing acidic byproducts called ketones. This buildup of ketones in the blood causes the dangerous metabolic state of acidosis, which can present with symptoms like excessive thirst, frequent urination, nausea, vomiting, and a fruity odor on the breath.
Hyperosmolar Hyperglycemic State (HHS) is generally seen in people with Type 2 diabetes, involving extremely high blood sugar levels, often exceeding 600 mg/dL. This extreme glucose concentration causes severe dehydration as the body tries to excrete the excess sugar through urine. The massive water loss and resulting concentrated blood lead to hyperosmolarity, which can cause significant neurological symptoms, including profound lethargy, confusion, and sometimes coma. Unlike DKA, HHS typically does not involve the production of large amounts of ketones or severe acidosis.
Emergency Steps for Blood Sugar Imbalances
Immediate action is necessary to correct blood sugar imbalances and prevent severe complications. For mild to moderate hypoglycemia, the standard protocol is often referred to as the “Rule of 15.” This involves consuming 15 grams of a fast-acting carbohydrate, such as four ounces of fruit juice, a tablespoon of honey, or three to four glucose tablets.
After consuming the fast-acting carbohydrate, the individual should wait 15 minutes and then recheck their blood sugar level. If the reading is still below 70 mg/dL, consuming another 15 grams of carbohydrate and waiting 15 minutes should be repeated. This cycle continues until the glucose level is safely above the danger threshold.
For severe hyperglycemia, particularly when blood sugar is consistently over 300 mg/dL, the primary focus is to monitor for signs of DKA or HHS. Individuals should check for ketones in their urine or blood if available, as a positive result indicates the body is breaking down fat for fuel. The person should drink plenty of water to combat dehydration and administer corrective insulin doses as prescribed. Immediate medical attention is required if the person is unable to keep fluids down, experiences persistent vomiting, is difficult to arouse, or loses consciousness.