My fasting sugar is normal, doctor — so my diabetes is under control, right? I hear this often. And the answer, unfortunately, is: not necessarily. Blood sugar control is complex, and a single fasting reading can give a misleading picture. Understanding the difference between fasting sugar and HbA1c is one of the most important things a diabetic patient can know.
Fasting Blood Sugar: A Snapshot
Fasting blood sugar (FBS) is a measurement of your glucose level after 8–12 hours without food. It tells you what your sugar is at one specific moment — typically early morning, before breakfast. Normal is below 100 mg/dL; diabetes is 126 mg/dL or higher.
The problem: your sugar fluctuates enormously throughout the day. It spikes after every meal. A fasting reading gives you just one data point — the overnight resting level. Many patients have perfectly normal fasting sugar but very high post-meal spikes that are causing damage.
HbA1c: The 3-Month Average
HbA1c (Glycated Haemoglobin) is fundamentally different. It measures the percentage of haemoglobin (red blood cell protein) that has glucose attached to it. Since red blood cells live for about 3 months, HbA1c reflects your average blood sugar level over the past 2–3 months — not just right now.
Why HbA1c Is the More Important Measure
HbA1c is the gold standard for assessing how well diabetes is actually controlled. A patient can diet strictly the day before a fasting test and get a good reading — but they cannot "cheat" an HbA1c. It captures the full picture: good days and bad days, dietary slips, lifestyle patterns, and whether the medication is truly working.
I monitor HbA1c in every diabetic patient every 3 months. If it's above 7% (the general target for most patients), I review medication and lifestyle together.
🩺 Both Tests Together Is Best
In my practice, I use both fasting sugar and HbA1c together. Fasting sugar helps me understand day-to-day patterns; HbA1c tells me the longer story. Post-meal glucose testing (PP sugar, 2 hours after meals) is also valuable — particularly for patients who have normal fasting but high HbA1c.
Know Your HbA1c Today
If you're diabetic and haven't checked HbA1c in the last 3 months, book a review. It's the most important number in your diabetes management.