‘Why are my HbA1C results 4.0 but FBS 121? The first test results were 4.3 and 111’

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3 min readNew DelhiApr 22, 2026 06:00 AM IST

Is it a concern when HbA1C rises and fasting blood sugar, or FBS, comes down? To get an informed insight on a Quora query asking the same: Why are my HbA1C results 4.0 but FBS 121? The first test results were 4.3 and 111; we reached out to an expert.

Dr Pranav Ghody, consultant endocrinologist and diabetologist at Wockhardt Hospitals, Mumbai Central, said that at first glance, this seems contradictory, but it can happen. “HbA1c shows your average blood sugar over the past 2 to 3 months, while fasting blood sugar is just one reading at a specific time. A normal or low HbA1c with a higher fasting value may mean that your overall sugar levels are generally well-controlled, but there can be occasional spikes, especially in the early morning,” said Dr Ghody.

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.

Should this be a cause for concern?

An FBS of 121 mg/dL is in the prediabetes range, so it shouldn’t be ignored, stressed Dr Ghody. “Even if HbA1c looks reassuring, consistently elevated fasting sugar may signal an early warning of glucose imbalance. It’s crucial not to rely on a single measurement; both readings together provide a clearer picture.”

Causes

One common explanation is the dawn phenomenon, which describes a natural rise in blood sugar during the early morning hours due to hormonal changes, such as cortisol and growth hormone. “This can lead to higher fasting levels even if your daytime sugars remain normal, which keeps HbA1c in a lower range,” said Dr Ghody.

diabetes Should you be concerned? (Photo: Freepik)

Are there other reasons for this mismatch?

There are a few possibilities. “Lab variation or pre-test factors, such as poor sleep, stress, late-night meals, or even illness, can temporarily raise fasting glucose. In some cases, conditions that affect red blood cells, like anemia or recent blood loss, can falsely lower HbA1c, making it look better than it actually is. So, it’s important to interpret the numbers in context,” elucidated Dr Ghody.

quora query Here’s what you should consider (Photo: Quora)

What to do?

Instead of jumping to conclusions, repeat the tests to confirm the pattern. You might also benefit from additional checks like post-meal blood sugar or continuous glucose monitoring to understand trends.

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“Focus on lifestyle basics: balanced meals, early dinners, good sleep, and stress management, as these can greatly affect fasting glucose. If the pattern continues, a detailed evaluation can help find the root cause and guide the right approach,” said Dr Ghody.