blood glucose
Blood glucose is simply the amount of sugar circulating in the bloodstream at any moment — the body's readily available fuel, delivered to every tissue by the blood. It is the single most tightly regulated metabolic variable, because too little starves the brain while too much slowly damages blood vessels and nerves.
In a healthy person, fasting blood glucose sits roughly between 70 and 100 milligrams per deciliter (about 3.9 to 5.6 millimoles per liter), rising modestly after meals and returning toward baseline within a couple of hours. The pancreas holds it in this narrow band by balancing insulin against glucagon, with longer-range help from counter-regulatory hormones.
Blood glucose is the headline number in diabetes care, but it is a snapshot: it swings with meals, activity, illness, and stress. That is why clinicians complement spot readings with HbA1c, which reflects average glucose over weeks, and increasingly with continuous glucose monitoring that reveals the full pattern of highs and lows.
Glucose is measured in different units worldwide: milligrams per deciliter in the United States and many countries, millimoles per liter in much of Europe and Asia. To convert mg/dL to mmol/L, divide by about 18.