3 min readNew DelhiMar 17, 2026 06:00 AM IST
Both HbA1c and fasting blood glucose are important tests, but they serve different purposes in understanding blood sugar levels. So, which is most important? As we came across this query on Quora: ‘What’s more important for diagnosing and monitoring diabetes: HbA1c or Fasting Blood Glucose (FBG)?’, we decided to seek an expert’s insight.
Fasting Blood Glucose (FBG) measures the level of glucose in the blood after an overnight fast, usually 8 to 10 hours. It shows the body’s blood sugar status at that specific moment. Due to this, Dr Pranav Ghody, consultant endocrinologist and diabetologist, Wockhardt Hospitals, Mumbai Central, said that FBG is often one of the first screening tests used to identify potential diabetes or prediabetes. “It is simple, quick, and effective for detecting issues with fasting glucose regulation. However, it can vary from day to day due to factors such as stress, illness, sleep, diet from the previous day, or even certain medications,” said Dr Ghody.
HbA1c provides a broader and more stable perspective, said Dr Ghody.
“This test measures the percentage of glucose attached to haemoglobin in red blood cells and reflects average blood sugar levels over the previous two to three months. For this reason, HbA1c is commonly used to assess long-term glucose control in individuals already diagnosed with diabetes. It helps doctors see whether blood sugar levels have been consistently high, even if a single fasting test appears normal,” said Dr Ghody.
So, instead of viewing one as more important, it helps to see them as complementary tools that together provide a clearer picture of metabolic health, said the expert.
“There are instances where one test may give more useful information than the other. For example, HbA1c is often more reliable for long-term monitoring and treatment adjustments. FBG is helpful for routine screening, early detection, and evaluating how well the body manages glucose overnight,” said Dr Ghody.
Here’s what an expert says (Photo: Getty Images/Thinkstock)
However, both tests have their limitations. “HbA1c can sometimes be influenced by conditions that affect red blood cells, such as anaemia or certain blood disorders. Similarly, fasting glucose alone may overlook individuals whose sugar levels rise significantly after meals,” said Dr Ghody.
Story continues below this ad
In practice, doctors often look at both values together, along with post-meal glucose levels and clinical symptoms. When combined, these tests help provide a more complete understanding of a person’s blood sugar patterns and guide appropriate treatment decisions.
DISCLAIMER: This article is based on information from the public domain and/or the experts we spoke to. Always consult your health practitioner before starting any routine.
