The abbreviation “BG” stands for Blood Glucose. Glucose is a simple sugar derived primarily from dietary carbohydrates and serves as the body’s main source of energy. This sugar is transported via the blood to every cell, fueling all necessary metabolic processes. Maintaining this level within a narrow, healthy range is tightly regulated, as fluctuations can have immediate and long-term effects on health.
The Essential Function of Blood Glucose
Glucose is the preferred fuel source for nearly all cells, which extract it from the blood to generate adenosine triphosphate (ATP), the cell’s energy currency. Circulating glucose originates mainly from the breakdown of dietary carbohydrates in the digestive system. The brain relies heavily on a constant supply of glucose because it cannot store it efficiently or use fat for energy. Red blood cells also depend exclusively on glucose for their energy needs. When the body requires energy, glucose is delivered through the circulatory system to active tissues like muscle cells, especially during physical exertion.
Interpreting Blood Glucose Levels
The concentration of blood glucose is measured in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L). Specific ranges are defined for health.
For a person without diabetes, a normal fasting level (no food intake for at least eight hours) is between 70 and 99 mg/dL (3.9 to 5.5 mmol/L). After a meal, levels rise but remain below 140 mg/dL (7.8 mmol/L) within two hours.
When blood glucose falls below 70 mg/dL, the condition is called hypoglycemia. Symptoms include shakiness, dizziness, and confusion, as the brain is deprived of its primary fuel source. Conversely, consistently high levels are known as hyperglycemia.
Sustained hyperglycemia, a hallmark of untreated diabetes, leads to serious long-term health complications. Chronic high glucose damages blood vessels and nerves, contributing to kidney disease, nerve damage, and vision problems. A fasting level between 100 and 125 mg/dL (5.6 to 6.9 mmol/L) is classified as prediabetes, indicating a higher risk of developing type 2 diabetes.
Methods for Measuring Blood Glucose
Blood glucose is routinely measured using several distinct methods to assess a person’s glucose status. The most common method for self-monitoring is point-of-care testing using a blood glucose meter. This involves pricking the fingertip with a small needle, called a lancet, to obtain a drop of capillary blood, which is then applied to a test strip.
For clinical diagnosis and accurate baseline measurements, a venous plasma glucose test is performed by drawing a blood sample from a vein and sending it to a laboratory. Newer technology includes Continuous Glucose Monitors (CGMs). These devices use a small sensor inserted under the skin to measure glucose in the interstitial fluid, providing a dynamic view of trends throughout the day and night.
The Body’s System for Regulating Glucose
The body maintains a stable blood glucose level through a hormonal feedback loop managed by the pancreas. Specialized cells within the pancreas, called the islets of Langerhans, monitor glucose concentration and release counter-regulatory hormones.
When blood glucose rises after a meal, the beta cells release insulin. Insulin signals cells to absorb glucose from the bloodstream and instructs the liver to convert excess glucose into glycogen for storage, lowering the circulating sugar level.
If blood glucose levels drop too low, the alpha cells release glucagon. Glucagon signals the liver to break down stored glycogen back into glucose and release it into the blood, a process called glycogenolysis. This opposing action ensures glucose homeostasis, keeping the body’s energy supply consistent.