Testing fasting blood glucose is an important indicator for judging whether blood sugar levels are normal. Routine health examinations generally include this test, which is conducted at a hospital or health examination center. However, in such cases, the blood sugar measured may not be true fasting blood glucose. Why is that? How should we interpret the test results?
First, let’s understand the definition of fasting blood glucose. Simply put, it refers to blood sugar levels in a resting state after not eating for 8 to 12 hours. It’s important to note there are two conditions: one is not eating, and the other is being in a resting state. Not eating is easy to understand; it means not consuming food that can be converted into blood sugar. Drinking water does not provide blood sugar, so it’s acceptable to drink water, but not excessively. The resting state means that apart from maintaining basic physiological activities, there should not be any additional physical activities that consume energy, such as morning exercises, tidying up, or preparing breakfast.
From this, we can deduce that only the blood glucose measured after a night’s sleep, right when one wakes up in the morning, is considered true fasting blood glucose. If after getting up, one engages in activities like making the bed, cleaning, preparing breakfast, or even morning exercises, the body will often utilize stored blood sugar for energy, meaning that the blood sugar level measured is no longer the blood sugar from a resting state. At this point, the measured blood sugar can only be referred to as pre-breakfast blood sugar, which may be higher or lower than the fasting blood sugar.
Therefore, the correct method for measuring fasting blood glucose is to check it immediately upon waking in the morning. Fasting blood glucose represents the baseline level of blood sugar for the entire day and is one of the main references for formulating blood sugar control plans. Inaccurate fasting blood glucose levels will undoubtedly mislead the creation of such plans.
Some might ask, what if blood sugar tests at hospitals are conducted after work starts at 8:00 AM?
In medicine, a glucose tolerance test combined with an insulin release test is used to rule out and diagnose diabetes. This involves measuring blood sugar levels before eating in the morning, and then after consuming 200 grams of steamed bread or 75 grams of glucose water after half an hour, one hour, and two hours, along with tracking corresponding insulin secretion. This method minimizes the inconsistencies between fasting blood glucose and pre-breakfast blood sugar levels. Hence, when diagnosing diabetes, conclusions cannot be solely drawn from fasting blood glucose; further tests, as mentioned, are required. For daily monitoring of fasting blood glucose in diabetic patients, it is sufficient to grasp the fasting blood glucose level based on measurements taken after waking up without engaging in extensive physical activity.
It is important to note that for individuals without diabetes, when undergoing fasting blood glucose tests at a hospital or health examination center, if the blood sugar exceeds 5.6mmol/L, even though it does not surpass the normal threshold of 6.1mmol/L, it suggests that there may be abnormal blood sugar levels. Increased monitoring of blood sugar levels is necessary, particularly checking the blood sugar two hours after meals, because if fasting blood glucose or pre-meal blood glucose is above 5.6mmol/L, it indicates that the body’s blood sugar regulation mechanisms may be starting to fail. More than half of individuals may show normal fasting blood glucose while having elevated blood sugar levels two hours after meals.
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