Hypoglycemia, or low blood sugar, occurs when blood glucose levels drop below the normal range, typically below 70 mg/dL (3.9 mmol/L). Glucose is the body’s primary energy source, especially for the brain. When levels fall too low, body systems are affected, requiring prompt investigation and management. Understanding the underlying cause is important for effective treatment and preventing complications.
Recognizing the Signs
The symptoms of low blood sugar can appear rapidly and vary among individuals. These symptoms are generally categorized into two types: autonomic (or adrenergic) and neuroglycopenic. Autonomic symptoms are the body’s initial response, triggered by hormones like adrenaline to raise glucose levels. These include shakiness, sweating, a rapid heartbeat, anxiety, and hunger.
As blood sugar levels continue to drop, the brain, which relies heavily on glucose, begins to lack fuel, leading to neuroglycopenic symptoms. These include confusion, dizziness, blurred vision, difficulty concentrating, slurred speech, and unusual behavior that might be mistaken for intoxication. In severe cases, prolonged low blood glucose can lead to seizures, loss of consciousness, or even coma. Seek medical attention immediately if these symptoms are experienced, especially if you do not have diabetes or if treatment for known diabetes is not resolving the symptoms.
Confirming Low Blood Sugar
When hypoglycemia is suspected, healthcare professionals first confirm low blood sugar by measuring glucose levels. This is a fundamental step, as symptoms alone can be misleading. Blood glucose can be quickly checked using a finger-prick test for an immediate reading, or through a laboratory blood draw for more precise confirmation.
The classic diagnostic criteria for hypoglycemia involve Whipple’s Triad. This triad consists of three conditions: observing symptoms consistent with hypoglycemia; measuring a low plasma glucose concentration at the time these symptoms occur (typically below 70 mg/dL, though symptoms may appear at 55 mg/dL or lower); and noting the resolution of these symptoms once the blood glucose level is raised. Fulfilling these criteria helps distinguish true hypoglycemia from other conditions with similar symptoms but no low blood sugar.
Investigating the Underlying Cause
Once low blood sugar is confirmed, identifying its specific cause is the next step, as treatment strategies depend on the root issue. The investigation begins with a thorough medical history, including current medications, dietary habits, alcohol consumption, and any existing medical conditions. Medications like insulin or sulfonylureas are common causes of hypoglycemia in individuals with diabetes.
Distinguishing between reactive (postprandial) hypoglycemia and fasting hypoglycemia is an important initial consideration. Reactive hypoglycemia occurs within a few hours after eating, while fasting hypoglycemia happens when a person has not eaten for an extended period. This distinction guides further diagnostic testing.
Specific diagnostic tests pinpoint the cause. For suspected fasting hypoglycemia, a prolonged supervised fast, typically up to 72 hours, is often used. During this inpatient test, blood glucose levels are monitored, and if symptoms develop, blood samples are collected to measure insulin, C-peptide, and proinsulin levels. Insulinoma, a rare pancreatic tumor, can be indicated by inappropriately elevated insulin, C-peptide, and proinsulin levels during a hypoglycemic episode, along with low beta-hydroxybutyrate levels. C-peptide and proinsulin levels help distinguish between the body’s own insulin production and external insulin administration.
Screening for sulfonylurea levels is also conducted to rule out the surreptitious use of these diabetes medications, which can induce hypoglycemia. Beyond pancreatic causes, other systemic illnesses can lead to low blood sugar, including adrenal insufficiency, liver, and kidney diseases. Adrenal insufficiency involves insufficient cortisol, a hormone regulating blood sugar. Liver and kidney diseases can impair glucose production or excretion. Tests for these conditions, such as cortisol levels or liver function tests, may be performed.
If an insulinoma or other pancreatic tumor is suspected, imaging studies may be used to locate it. Non-invasive methods like computed tomography (CT) scans and magnetic resonance imaging (MRI) can be used, though their effectiveness varies as many insulinomas are small. Endoscopic ultrasound (EUS) is a more invasive but often more accurate imaging technique for localizing small pancreatic lesions. Investigations progress based on the individual’s symptoms and initial findings to identify the cause of hypoglycemia.