Why blood sugar readings may look confusing: Patient had slightly high fasting blood glucose of 107 mg/dL but HbA1c was too high, above 7%

 

Source: https://indianexpress.com/article/health-wellness

Blood glucose tests are important tools to understand how well your body is managing glucose. Sometimes, though, the results can be confusing. For example, a patient showed me he had a fasting blood glucose of 107 mg/dL (which looks only slightly above normal), but the HbA1c (average blood sugar count of three months) was above 7 per cent (which is clearly in the diabetic range, the normal being 5.7 per cent). How can this happen and what does it mean? Let’s break it down in simple terms.

Fasting Blood Glucose (FBS): This test measures your blood glucose at a single point in time, after you have not eaten for at least eight hours.

Normal: less than 100 mg/dL

Prediabetes: 100–125 mg/dL

Diabetes: 126 mg/dL or higher

So, a fasting glucose of 107 mg/dL means the person is in the prediabetes range.

HbA1c (Glycated Hemoglobin): This test reflects your average blood glucose over the past two to three months. It shows how much glucose has been sticking to your red blood cells.

Normal: less than 5.7%
Prediabetes: 5.7–6.4%
Diabetes: 6.5% or higher

An HbA1c of over 7 per cent indicates sub-optimally controlled diabetes, with average blood glucose around 170–180 mg/dL.

Why do the results differ?

This mismatch happens more often than you might think. Remember that blood glucose rises after meals or what we call post-prandial spikes. Fasting glucose may look almost normal but after eating, the person’s glucose may rise very high. These repeated spikes raise the HbA1c, even though fasting numbers look okay.

Fasting glucose is just one snapshot and may reflect recent improvement in glucose levels. HbA1c shows the bigger picture over months and will be influenced by the glucose pattern of the last three months. Some people first develop high glucose after meals (postprandial hyperglycemia) before fasting glucose goes up.

Rarely, conditions like anemia, thalassemia, kidney disease or certain medications can affect HbA1c readings.

What does this mean for the patient?

The HbA1c reading of over 7 per cent cannot be ignored. It means that overall blood glucose has been consistently high, even if the fasting reading looks only mildly elevated. This person does have diabetes and needs lifestyle changes and possibly medication. Fasting glucose of 107 mg/dL may give a false sense of security, but HbA1c is more reliable for long-term risk.

Why is this important?

Uncontrolled blood glucose, reflected in a high HbA1c, increases the risk of heart disease and stroke, kidney damage, nerve problems (neuropathy), eye damage (retinopathy) and slows down wound healing. Early diagnosis and management can prevent these complications.

What should be done?

Sometimes doctors repeat the tests or add an Oral Glucose Tolerance Test (OGTT) to be sure. Review your lifestyle. Eat a balanced diet with less glucose and refined carbs. Exercise at least 30 minutes a day, five days a week. Maintain a healthy weight. If lifestyle changes alone don’t help, doctors may prescribe medicines like metformin or others depending on the case. Keep checking blood glucose and HbA1c to track progress. Fasting tests can sometimes miss the bigger picture but HbA1c reveals how glucose behaves over months.