Many
people only pay attention to fasting blood glucose during physical
examinations, and they think their blood glucose is completely normal as long
as the value is below 6.1 mmol/L.
However, it is not widely known that diabetes screenings only test for fasting blood glucose, which can easily miss a type of latent hyperglycemia. By the time symptoms appear, the function of the pancreatic islets has already been quietly compromised.
Dr. Hou Zeling from the Endocrinology Diagnosis and Treatment Group of Hainan Chengmei Hospital reminds us that normal fasting blood glucose does not mean no diabetes, and many people fall into the trap of postprandial blood glucose.
Fasting blood glucose level is 5.8mmol/L, and type 2 diabetes has been diagnosed
Mr. Chen, 52 years old, attends his unit's physical examination every year, and his fasting blood glucose levels have been consistently between 5.6 and 5.8 mmol/L. The reference range indicated on the report is normal, so he has always believed that his blood glucose levels are healthy.
Occasionally experiencing dry mouth and fatigue, he attributed it to old age and exhaustion from staying up late, and never underwent further blood glucose-related examinations.
Half a year ago, Mr. Chen noticed a significant increase in fatigue, an increased thirst for water, and an unexplained weight loss of 4 kilograms. This prompted him to seek medical attention at the endocrinology department.
After a careful inquiry, the doctor did not just check his fasting blood glucose, but arranged an oral glucose tolerance test (OGTT) and a glycated hemoglobin test.
After the results came out, Mr. Chen was shocked: his fasting blood glucose was 5.78 mmol/L, still within the normal range; however, his postprandial blood glucose two hours after a meal was as high as 11.6 mmol/L, and his glycated hemoglobin was 7.2%. Taking into account his medical history, he was diagnosed with type 2 diabetes.
Mr. Chen was puzzled: his fasting blood glucose was clearly not over the limit, so how could he have diabetes? The doctor explained that this was a very typical case of isolated postprandial hyperglycemia, which was also the most easily missed type of diabetes.
Why is it that fasting blood glucose is normal, but postprandial blood glucose exceeds the standard?
According to Dr. Hou Zeling, the body regulates blood sugar in two stages. In a fasting state, basic insulin can barely stabilize blood sugar; however, after a meal, a large amount of carbohydrates enter the bloodstream, and the insulin secreted by the pancreatic islets cannot keep up with the rapid rise in blood sugar, leading to a surge in postprandial blood sugar.
The characteristics of this group of people are quite subtle:
✅ Fasting blood glucose < 6.1 mmol/L, as indicated as normal on the physical examination report
✅ Postprandial blood glucose is elevated, but there is no obvious discomfort at ordinary times
✅ Commonly seen in middle-aged people, those with abdominal obesity, hypertension, hyperlipidemia, and those with a family history of diabetes
According to the diagnostic criteria for diabetes:
1. Fasting blood glucose ≥7.0 mmol/L can be diagnosed as diabetes;
2. If the blood glucose level is ≥11.1 mmol/L 2 hours after a 75g oral glucose tolerance test (OGTT), the diagnostic criteria for diabetes can be met;
3. A glycated hemoglobin level of ≥6.5% is also an important diagnostic basis.
Many people only undergo fasting blood glucose testing during their physical exams, skipping postprandial blood glucose testing altogether. As a result, a significant number of individuals with "postprandial hyperglycemia" are missed. Dr. Hou Zeling emphasizes that a normal fasting blood glucose level only represents the baseline blood glucose status and does not reflect the body's ability to regulate blood glucose after eating. Persistent postprandial hyperglycemia can cause ongoing damage to blood vessels, the fundus of the eye, kidneys, and nerves. Complications will not be avoided just because fasting blood glucose levels are normal.
Another group of people is in the prediabetes stage, with a fasting blood glucose level of 5.6~6.1 mmol/L, which is classified as impaired fasting glucose. At this point, postprandial blood glucose is likely to have already exceeded the normal range. This is the golden window for intervention, and seizing this opportunity can delay or even reverse the progression to diabetes.
Who should not only check fasting blood glucose?
Dr. Hou Zeling suggests that for the following high-risk groups, physical examinations should not only measure fasting blood glucose, but also include a complete OGTT or postprandial 2-hour blood glucose test, as well as glycosylated hemoglobin examination.
1. Age ≥ 40 years old;
2. Overweight or obesity, especially with a large belly and abdominal obesity;
3. Suffering from hypertension, hyperlipidemia, fatty liver, and hyperuricemia;
4. Immediate family members have diabetes;
5. Women with a history of gestational diabetes or delivery of macrosomia;
6. Sitting for long periods with little physical activity, and consuming high-calorie diets for an extended period;
7. Recurrent skin infections, itching, blurred vision, and limb numbness.
Dr. Hou Zeling emphasizes that just because many people do not exhibit the typical symptoms of "three increases and one decrease" does not mean their blood sugar levels are safe. Occult hyperglycemia can silently damage blood vessels, and by the time symptoms such as numbness in hands and feet, vision loss, and kidney disease appear, the damage is mostly irreversible.
What should you do if your blood sugar is high after meals?
If postprandial blood glucose is found to be elevated, there is no need for excessive panic. Dr. Hou Zeling provides several practical intervention plans:
1. Adjust the dietary structure by focusing on staple foods
Avoid consuming refined rice and white flour as the sole source of nutrition. Instead, pair them with miscellaneous grains and beans, as well as green vegetables, meat, eggs, and fish. This will slow down the absorption of carbohydrates, stabilize postprandial blood sugar levels, and help you feel seven-tenths full after each meal. Try to limit your intake of porridge, sweet drinks, and pastries.
2. Moderate exercise after meals
Taking a half-hour break after meals and going for a brisk walk for 20 to 30 minutes can effectively lower postprandial blood glucose levels. It is not recommended to engage in strenuous exercise on an empty stomach.
3. Regular monitoring and standardized medical visits
One should not make a judgment based solely on a single result. If abnormalities are found, seek medical consultation at a specialized endocrinology clinic. The doctor will assess the function of the islets of Langerhans and determine whether it is prediabetes or diabetes. Do not self-medicate by purchasing medications.
4. Weight management
Weight loss is the most effective way to improve insulin resistance. For individuals with abdominal obesity, a 5% to 10% reduction in body weight often leads to significant improvement in blood glucose levels.
Dr. Hou Zeling expressed her sentiment that she often encounters such patients in clinical practice, who have normal fasting blood glucose levels during annual physical examinations but have quietly developed diabetes. When examining blood glucose levels during physical examinations, one should not solely focus on the fasting indicator.
The screening for diabetes involves a comprehensive assessment of fasting blood glucose, postprandial blood glucose, and glycosylated hemoglobin. One should not be misled by the illusion of "meeting the fasting criteria", especially for high-risk groups. A complete set of blood glucose assessments should be conducted to facilitate early detection and intervention, thereby reducing the risk of complications.
Expert Introduction
Hou Zeling, Attending Physician
Medical expertise: Specialized in the diagnosis and treatment of diabetes and related complications, as well as thyroid diseases such as hyperthyroidism, hypothyroidism, and thyroiditis. Additionally, proficient in the diagnosis and treatment of common endocrine diseases such as obesity, gouty arthritis, lipid metabolism disorders, electrolyte metabolism disorders, and primary aldosteronism.