Why is my Fasting Blood Sugar High, but my A1c is Normal?

Medically Reviewed By DR. DWARAKANATH C.S March 28, 2024

For the diagnosis of diabetes, doctors generally suggest multiple tests, including a fasting blood sugar test, postprandial blood sugar test, and HbA1c test. However, sometimes, due to factors like present medical conditions or co-morbidities, ongoing medications, nutrient deficiency, etc.,  the test values may be affected. Individuals, including some who may be non-diabetic, may get readings that may not reflect their actual test values. There may be cases where one may get high A1c test results yet normal blood sugar readings and vice versa. So, in this blog, we discuss in detail the possible reasons that affect your blood sugar test readings. So, let’s begin!

What is an HbA1c Test?

HbA1c stands for Hemoglobin A1c, which is a type of hemoglobin found in red blood cells. When glucose in the blood gets as hemoglobin, it forms glycated hemoglobin (HbA1c). The amount of HbA1c formed is directly proportional to the glucose in the blood.

The HbA1c test provides an average blood sugar level over the past two to three months. This is because the lifespan of red blood cells is about that long. This test becomes a valuable tool for analysing long-term blood sugar control in diabetics.

For people without diabetes, the normal range for HbA1c is typically less than 5.7%. In diabetic patients, the target A1c level varies depending on different factors including your age, overall and present health, and present medical conditions. However, generally, a lower HbA1c level indicates better blood glucose control and a lessened risk of having diabetes-related complications.

The HbA1c test is typically performed in a lab with the blood sample obtained from a vein in the hand. It’s a fast and relatively less painful procedure that doesn’t require any special preparation. Results are usually available within a few days.

Read More: Connections Between Diabetes and Hypertension.

What are Safe A1c Levels?

What are Safe A1c Levels?

Safe A1c levels are different for non-diabetics and diabetics. According to the National Institute of Health, for a non-diabetic patient, the HbA1c level should be below 5.7% or 39 mmol. Further, A1c in the range of 5.7% to 6.4 % or 39 mmol to 46 mmol is considered prediabetes range. According to the Centers for Disease Control and Prevention, A1c level above 6.4% or 48 mmol indicates diabetes.

But is the safe range of A1c for diabetes patients? According to the Better Medicine website, the A1c target range for most diabetes patients should be close to 7% or 53 mmol. Keeping your HbA1c level in this range is acceptable for doctors/diabetologists, but do remember the lower the HbA1c, the better it is for a diabetes patient. Along with this, if you have good glycemic control, it will help you control diabetes more effectively.

However, for some diabetes patients, individualised targets may be set based on factors such as age, present health conditions, and risk of hypoglycemia (low blood sugar). They may have different target A1c levels, which can be higher than 7%. The doctor/diabetologist will be the best judge to determine your safe or target A1c level.

Read More: Can Type 2 Diabetes be Reversed Permanently?

Why is my Fasting Blood Sugar High, but my A1c is Normal?

There can be cases where fasting blood glucose can be in the higher range, indicating prediabetes or diabetes. However, the HbA1c is in the normal non-diabetic range. The fasting blood glucose measures your blood sugar level at a particular point in time. Therefore, it is more likely to get disturbed by your daily and weekly activities. The following can be the possible reasons:

Lack of proper sleeping cycle

It is clinically proven that lack of sleep can affect your glucose metabolism in your body. Individuals with poor sleeping patterns are seen to have deteriorated insulin response to food. Some studies show individuals with poor sleep had higher blood sugar and insulin post their first meal compared to those who had good sleep of 8 hours. Insulin resistance is seen higher in people with uneven and poor sleep patterns.


Your body has a hormone called cortisol that has a flight-or-fight response. This hormone helps you counteract stressful situations. The cortisol hormone regulates blood glucose release. It does so by breaking glucose into glycogen, in which form it is stored. There is a high chance that when you are under stress, your blood sugar level can inflate. So, your fasting blood sugar will vary in stress and no-stress situations.


Food can greatly influence your blood sugar levels. Therefore, doctors recommend having at least a 12-hour window before going for a fasting blood sugar test. You can only drink water during this period, not even black coffee or tea. Every individual’s body reacts differently to coffee and tea, and this can affect your blood sugar readings.

When you have High Hba1c but Normal Fasting Glucose

There can be cases where you have high A1c but normal fasting glucose and are non-diabetic. This is because the HbA1c test gauges the glucose present in the haemoglobin. The number of factors that influence haemoglobin can influence the reading, too.

A deficiency of certain specific nutrients can inflict a rise in HbA1c. These include iron, folate, and vitamin B-12. So, a deficiency of these nutrients can elevate your HbA1c levels. So, if you have the following conditions, do get in touch with the doctor. Your doctor and you will have to closely work and monitor your readings and develop a practical treatment course.

Read More: Know About Good Foods for Prediabetes

Reasons you can have High Hba1c But not Diabetes

Reasons you can have High Hba1c But not Diabetes

The following are factors that can make your HbA1c levels high without diabetes:


Anemia occurs when you have iron deficiency; also, you may have folate and vitamin B12 deficiency. According to a study conducted by the Diabetes Journal, individuals with anemia had much greater incidents of high A1c levels. The study further categorised individuals gender-wise. It found women with anemia had way higher A1c readings than usual.

Kidney and Liver Disorders

Kidney patients may find it hard to rely on the readings of their A1c tests. Individuals with kidney ailments are more susceptible to complications like anaemia and other nutrient deficiencies, as well as kidney failure. According to the NIH website, all these affect the result of the HbA1c test.

In case one has liver disorders, the HbA1c test will not precisely predict the glycemic control due to the RBCs (Red blood cells) being affected.

Certain Medication

According to the National Institute of Health, several medications can influence the reading of the A1c test. Some anti-retroviral drugs, aspirin, etc., can inflate your HbA1c test readings and prove them inaccurate. NIH reports that all these medicines that make your A1c high can cause hemolysis and may even interfere with glycation. Research conducted by the Indian Journal of Endocrinology and Metabolism suggests chronic excessive usage of certain medicines does influence and inflate and deflate your A1c levels.

Spleen related Disorders

According to the National Institute of Diabetes and Digestive and Kidney Diseases, spleen diseases like sickle cells or asplenia can affect your A1c readings. Studies by the National Institute of Health also show there can be a rise in HbA1c readings after the spleen removal procedure or splenectomy.

Low Thyroid Hormone Levels

According to the NIH, thyroid hormones affect your body’s metabolism and body’s rate of calorie usage. Also, the amount of thyroid hormones in the bloodstream influences the A1c readings. This can lead to potential inaccuracy in HbA1c test results. Low thyroid has been seen to elevate A1c.

Abnormal Haemoglobin Variants

There are multiple variants of hemoglobin, and the type can also affect your A1c test results. Generally, it has been observed that Type HbAs found in Africans tend to give false A1v readings. However, in India, the most common haemoglobin type is haemoglobin A.


According to research published by the National Institute of Health, there is a link between age and HbA1c in individuals with normal blood sugar and without diabetes. The study says the changes in glycation rate are associated with ageing and are responsible for the link between gae and HbA1c.

FAQs (Frequently Asked Questions)

Can you have high fasting blood sugar and not be diabetic?

Yes, you can have high fasting blood glucose and be non-diabetic. When you eat food rich in carbs and sugar, there may be a spike in your blood sugar, but since you are non-diabetic, the insulin hormone released by your body will regulate it. Also, factors like sleep deprivation and stress can inflate your fasting blood sugar.

Why is only my fasting blood sugar high?

High fasting blood sugar can be an indication that your body is unable to manage and regulate your blood sugar levels. This may be due to factors like insulin resistance, lessening of insulin production, or both.

Which is more accurate HbA1c or fasting glucose?

According to the epidemiological study published by the National Institute of Health, the fasting blood sugar(FBS) test is more accurate than the HbA1c test. The top reason is that HbA1c is more prone to be affected by other factors than the FBS test.

Last Updated on by Dr. Damanjit Duggal 


This site provides educational content; however, it is not a substitute for professional medical guidance. Readers should consult their healthcare professional for personalised guidance. We work hard to provide accurate and helpful information. Your well-being is important to us, and we value your feedback. To learn more, visit our editorial policy page for details on our content guidelines and the content creation process.

Leave a Reply

Download Free Diabetes Diet Plan