Here we will learn about ” Normal a1c but high fasting glucose”. A normal A1C level indicates the average blood sugar control over the past two to three months. It is generally used to diagnose and monitor diabetes. A high fasting glucose level, on the other hand, refers to an elevated blood sugar level after an overnight fast.

If you have a normal A1C but a high fasting glucose level, it can be due to several reasons but some are:

  • Impaired fasting glucose (IFG): It’s refers to a condition where blood sugar levels are higher than normal but not high enough to be considered diabetes. It can be an early indicator of prediabetes. In this case, your A1C level may not be significantly affected yet, but your fasting glucose levels are elevated.
  • Somogyi effect: The Somogyi effect, also known as rebound hyperglycemia, occurs when low blood sugar levels during the night trigger the release of stress hormones, leading to an increase in blood sugar levels in the morning.
    • This can result in higher fasting glucose levels despite relatively normal A1C levels.
  • Dawn phenomenon: It is characterized by a rise in blood sugar levels in the early morning hours. It occurs due to the release of hormones that counteract insulin’s effects, leading to elevated fasting glucose levels.
    • NOTE: This can happen even in individuals without diabetes or with well-controlled diabetes.
  • Lab error or temporary fluctuations: It’s possible that the high fasting glucose reading could be due to a laboratory error or temporary fluctuations in your blood sugar levels.
    • Confirmatory tests and further monitoring can help identify whether there is an ongoing issue.

Here’s the video of Normal a1c but high fasting glucose.

Normal fasting glucose but high a1c

If you have a normal fasting glucose level but a high A1C, it is indeed unusual, as the A1C test reflects the average blood sugar level over the past two to three months, while fasting glucose measures your blood sugar level after an overnight fast.

A high A1C typically indicates poor long-term blood sugar control, while a normal fasting glucose level suggests good blood sugar control in the short term. However, there are a few potential explanations for this discrepancy:

  • Recent changes in blood sugar levels: The A1C test reflects an average over several months, so if your blood sugar levels were previously elevated but have improved recently, your fasting glucose level might be normal while the A1C is still elevated due to the past high levels.
  • A1C’s limitations: While the A1C test is a valuable tool for assessing long-term blood sugar control, it is not perfect. Factors such as certain medical conditions, variations in red blood cell lifespan, and certain genetic factors can affect the accuracy of the A1C test and result in discrepancies with fasting glucose levels. 
  • Laboratory error: It’s possible that there was an error in the A1C test result. A repeat test can help confirm whether the initial reading was accurate.

What is Hba1c?

Hba1c is the short name for Glycated Hemoglobin. Such hemoglobin form when HB bind with glucose by non-enzymatic glycation pathway, by releasing plasma glucose into hemoglobin.

How is Hba1c synthesis in our body?

Hba1c is formed by the non-enzymatic glycation pathway, by releasing plasma glucose into hemoglobin

What is the limitation of the Hba1c test?

Hba1c test is limited to a three-month average because the lifespan of red blood cells is four months (120 days). However, since all red blood cells do not undergo simultaneous rupture, HbA1C is taken as a specific for three months.

why is my fasting blood sugar high but my a1c is normal?

A normal A1C indicates good long-term blood sugar control, while a high fasting blood sugar suggests elevated blood sugar levels after an overnight fast. This discrepancy could be due to recent changes in blood sugar levels, lab error.

what if a1c is normal but fasting glucose high?

If your A1C is normal but your fasting glucose is high, it could indicate a condition such as impaired fasting glucose, the dawn phenomenon, the Somogyi effect, temporary fluctuations.

what does it mean if your fasting glucose is high but your a1c is normal?

If your fasting glucose is high but your A1C is normal, it may indicate a temporary or recent increase in blood sugar levels. While A1C provides an average of blood sugar control over the past two to three months.
It can be due to dawn phenomenon, the Somogyi effect, temporary fluctuations.

what if my a1c is high?

If your A1C is high, it indicates that your average blood sugar levels have been elevated over the past two to three months. This could be a sign of poor blood sugar control and may suggest the presence of diabetes or prediabetes.

if my glucose is 120 what is my a1c?

The relationship between average blood glucose and A1C is not a direct conversion. However, an estimated A1C value of around 6.0% to 6.1% is often associated with a fasting glucose level of 120 mg/dL.

is a1c higher when fasting?

No, fasting itself does not directly impact A1C levels. A1C is a measure of average blood glucose levels over the past two to three months and is not influenced by short-term fasting.

how many hours fasting for hba1c?

Fasting is not required for an HbA1c test. The HbA1c test measures the average blood glucose level over the past two to three months.

how to calculate hba1c from fasting blood sugar?

To calculate an estimated HbA1c from a fasting blood sugar level:
1. Multiply the fasting blood sugar level by 28.7.
2. Subtract 46.7 from the result.
3. Divide the value obtained by 28.7.

6 thoughts on “Normal a1c but high fasting glucose (glycated-hemoglobin)”

  1. Awful article. It contradicts itself on so many levels.

    1st part:
    Normal a1c but high Fasting Glucose

    Normal a1c but high fasting glucose is the sign of Diabetes. This is the initial stage of diabetes Miletus because a1c shows the sugar level of previous weeks.

    2nd part:
    Fasting glucose high but a1c normal

    If somebody has high fasting glucose but Hba1c is below 5.7% or normal. He needs not worry about his/her health. Fasting glucose can be rise due to some hormonal imbalance a few times. This rise in sugar will decline after a few hours.

    Just awful.

  2. I understand that high fasting BG with normal HbA1C is an indicator of Diabetes. As the offshore Medic on my facility, I perform Fitness to Work Physical Examinations on a regular basis for our workgroup, for which blood testing (lipid profile, blood sugar, and HbA1C) are all a part. Having access to the equipment, I test my own approximately every 6 months.

    I am confused by my results. The high fasting BG (120-130mg/dl) began about 3 years ago, and has remained fairly constant. But the entire time period, the HbA1C has been 5.4-5.6%, no higher, no lower. I would think, if Diabetes were truly present, that I would see an increase in HbA1C readings by now.

    I exercise regularly, eat a fairly well balanced diet (I’ve cut out processed sugar, bread, and keep starches like rice and potatoes to a minimum) and continually strive to battle the scourge of the upper-50 yo male, the spreading waistline. It’s a bit of a mystery to me.

    • I was diagnosed with prediabetes with 5.8 A1C and 120 FBS thereafter I controlled my carb intake, resultantly my A1C came down to 5.5 and then 5.3 but still my FBS is ranging in 120s. I am worried about such results as if i had diabetes.
      I have lost 12 kg weight while continuously losing weight now i am worried about weight loss too. Is it due to walk, running and diet control due diabetes as the diabetic patient do face weight loss

      • Weight loss can be a symptom of diabetes, but it is not always the case. It is possible that your weight loss is due to your diet control and exercise routine, rather than diabetes. In fact, losing weight through a healthy diet and regular exercise is often recommended as a way to manage blood sugar levels and reduce the risk of developing diabetes.


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