Daily Blood Sugar Fluctuations and Diabetes Diagnosis: Criteria and Symptoms Explained

The characteristics of blood glucose fluctuations in a normal person throughout the day: Maintaining relatively constant blood glucose levels is extremely beneficial to human health, as it ensures normal glucose metabolism within tissue cells, thereby guaranteeing the normal functioning of tissues, organs, and life activities. The main characteristics of blood glucose fluctuations throughout the day are as follows: Blood glucose levels rise significantly one hour after a meal, generally reaching 7.8–8.9 mmol/L, with a maximum not exceeding 10.0 mmol/L. This is because the absorption of glucose in the intestines gradually increases after a meal, leading to elevated blood glucose. Stimulated by high blood glucose, pancreatic β-cells increase insulin secretion, using insulin to inhibit gluconeogenesis in the liver and promote the conversion of glucose into liver glycogen, which enters muscle, fat, and other tissues, thus blocking the source of glucose and accelerating glucose utilization to suppress the postprandial rise in blood glucose. Two hours after a meal, both blood glucose and plasma insulin levels drop back to normal. Since most people eat three meals a day, blood glucose levels will rise for approximately 18 to 6 hours within a 24-hour period.

Because insulin secretion decreases relatively during fasting, while glucagon secretion increases accordingly, it promotes glycogenolysis, increasing blood glucose levels. Simultaneously, it increases growth hormone secretion, inhibiting the utilization of glucose by various tissue cells.

Hypoglycemia generally does not occur in healthy individuals during fasting and is usually maintained within the normal range, i.e., when there is an adequate supply of glucose.

How to determine hyperglycemia? Understanding the diagnostic criteria for diabetes is crucial for monitoring blood glucose levels, observing treatment effectiveness, adjusting treatment plans promptly, and preventing or delaying the onset of complications.

The diagnostic criteria for diabetes mellitus are shown in the table below:

Item | Venous Blood Glucose

Fasting (mmol/L) (75 ml oral glucose)

2-hour Postprandial (mmol/L)

Normal | <6.1 | <7.8

Diabetes | ≥7.0 | ≥11.1 (or random blood glucose)

Impaired Glucose Tolerance (IGT) | <7.0 | 7.8～11.1

Imperfected Fasting Glucose Regulation (IFG)

6.1～7.0

<7.8

Note: "Random blood glucose" refers to blood glucose measured at any time, regardless of the time elapsed since the last meal. If there are no typical symptoms, blood glucose should be measured again on different dates. A diagnosis of diabetes can only be made if all measurements exceed the standards in the table.

Excessive Appetite

Due to significant urinary glucose loss, such as more than 500 grams of glucose per day, the body is in a state of semi-starvation, leading to increased appetite and food intake due to energy deficiency. Simultaneously, high blood sugar stimulates insulin secretion, causing patients to experience increased hunger and appetite, constantly feeling unsatisfied. They may even eat five or six meals a day, consuming 1-1.5 kg of staple food and significantly more side dishes than normal, yet still not satisfying their appetite.

Excessive thirst:Due to excessive urination, excessive water loss leads to intracellular dehydration, stimulating the thirst center and causing polydipsia (excessive thirst and frequent drinking) to replenish fluids. The more urine is excreted, the more water is consumed, forming a direct proportional relationship.

Excessive urination:Urine volume increases, reaching 3000-5000 ml per day, and can reach over 10000 ml in some cases. The frequency of urination also increases, potentially occurring every 1-2 hours, with some patients urinating more than 30 times per day. In diabetic patients, elevated blood glucose levels cannot be fully utilized by the body, especially as glomerular filtration is not completely reabsorbed by the renal tubules, leading to osmotic diuresis and polyuria. The higher the blood sugar, the more glucose is excreted in the urine, and the greater the urine volume.

Weight Loss: Due to insufficient insulin, the body cannot fully utilize glucose, accelerating the breakdown of fat and protein to replenish energy and calories. This results in the large consumption of carbohydrates, fats, and proteins in the body, coupled with water loss, leading to weight loss and emaciation. In severe cases, weight loss can reach tens of kilograms, causing fatigue, weakness, and lethargy. Similarly, the longer the disease duration and the higher the blood sugar, the more pronounced the weight loss.

Some patients with type 2 diabetes have atypical symptoms, only experiencing dizziness, weakness, or even no symptoms. Some may experience hypoglycemia before lunch or dinner in the early stages of the disease or before the onset of diabetes. The condition worsens under stress and may present with loss of appetite, nausea, vomiting, abdominal pain, increased urination, dizziness, drowsiness, blurred vision, difficulty breathing, and even coma.