HbA1c and Insulin Resistance: Using Glucose Metabolism as an Early Warning System

Type 2 diabetes often announces itself years in advance — before anyone diagnoses it. HbA1c and fasting blood glucose show you where you stand on that scale, and give you the chance to take action in time.

What HbA1c measures and why it differs from daily blood sugar

HbA1c stands for glycated haemoglobin — the share of red blood pigment that has permanently bonded with glucose. Because red blood cells circulate in the blood for about 8 to 12 weeks, the HbA1c value reflects the average of your blood glucose level over that period. A single sweet meal does not skew the result the way it can with fasting blood glucose.

The World Health Organization and the American Diabetes Association define an HbA1c below 5.7 percent (39 mmol/mol) as unremarkable. Values between 5.7 and 6.4 percent (39–47 mmol/mol) are classified as prediabetes; from 6.5 percent (48 mmol/mol) upwards, the term type 2 diabetes applies. These thresholds are pragmatic choices — but what is particularly interesting is what is already signalled within the upper normal range.

Prediabetes: the underestimated in-between stage

An HbA1c value in the prediabetes range does not mean you will fall ill soon. It means your body is already under pressure when processing glucose. Many people are unaware of this because prediabetes is often symptom-free. Estimates suggest that around 30 to 35 percent of adults over 50 in Germany and Switzerland are affected.

A 2010 study in the New England Journal of Medicine showed that HbA1c values between 5.5 and 6.0 percent can already be associated with a measurably elevated cardiovascular risk — even before the diabetes threshold is crossed. This makes HbA1c an early indicator that reaches far beyond blood sugar alone.

Insulin resistance: the mechanism behind it

Insulin is the hormone that signals cells to take up glucose from the blood. In insulin resistance, cells — primarily in muscle, liver and fatty tissue — respond increasingly weakly to this signal. The body initially compensates by having the pancreas produce more insulin. As long as this works, blood glucose stays normal and HbA1c remains unremarkable.

Only when the pancreas can no longer compensate adequately does blood glucose rise — and with it, HbA1c. Insulin resistance itself can therefore be measured long before blood glucose deviates. That is why the fasting insulin value, which is also absent from standard blood tests, can be so informative.

HOMA-IR: measuring insulin resistance directly

The HOMA-IR (Homeostatic Model Assessment of Insulin Resistance) calculates insulin resistance from two values measured simultaneously while fasting: blood glucose and insulin. The formula is: fasting insulin (µU/ml) × fasting blood glucose (mmol/l), divided by 22.5. A HOMA-IR below 1.0 is considered a favourable range; values above 2.5 are worth looking into more closely.

HOMA-IR is not determined routinely and needs to be specifically requested from your doctor. The combination of HbA1c, fasting blood glucose and fasting insulin provides a significantly more complete picture of glucose metabolism than any single value alone. Anyone thinking in terms of prevention should treat these three values as a panel that belongs together.

What the values mean and when you can take action

A slightly elevated HbA1c or HOMA-IR is not a verdict. Studies show that regular physical activity — especially strength and endurance training — can significantly improve insulin sensitivity. A fibre-rich diet and reducing heavily processed carbohydrates have also been shown to affect both markers.

An HbA1c in the upper normal range (5.3 to 5.6 percent) is a meaningful prompt for many people to reconsider their diet and exercise habits — not because a diagnosis is looming, but because the research shows that lifestyle changes are particularly effective at this stage. A conversation with your doctor will help clarify whether further diagnostics make sense.

Tracking glucose markers over time with the YUTHI app

In the YUTHI app you can enter your HbA1c, fasting blood glucose and HOMA-IR as soon as you have them. The trend across several measurements is more meaningful than any individual value — a slight improvement in HbA1c from 5.8 to 5.5 percent after three months of lifestyle changes is a clear signal that you can read directly in the app.

Sources

• American Diabetes Association. Classification and Diagnosis of Diabetes: Standards of Medical Care in Diabetes 2023. Diabetes Care, 2023;46(Suppl 1):S19–S40.
• Selvin E et al. Glycated hemoglobin, diabetes, and cardiovascular risk in nondiabetic adults. New England Journal of Medicine, 2010;362(9):800–811.
• Matthews DR et al. Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia, 1985;28(7):412–419.
• Petersen MC, Shulman GI. Mechanisms of insulin action and insulin resistance. Physiological Reviews, 2018;98(4):2133–2223.