Insulin resistance and A1c: what's the connection?

Insulin resistance is one of the earliest changes in the path toward prediabetes and type 2 diabetes — often present years before A1c or fasting glucose move out of the normal range. Understanding the connection helps explain why some people receive a prediabetes diagnosis seemingly "out of nowhere."

What insulin resistance actually means

Insulin is the hormone that allows glucose to move from the bloodstream into cells for energy. Insulin resistance means cells respond less effectively to insulin's signal, so the body compensates by producing more insulin to achieve the same effect. This compensation can keep blood glucose — and therefore A1c — looking normal for a long time, even as insulin resistance quietly worsens underneath.

Why A1c can lag behind

A1c and fasting glucose typically only start rising once the pancreas can no longer fully compensate with extra insulin production. This means someone can have significant, longstanding insulin resistance with an entirely normal A1c — the number simply hasn't caught up yet to what's happening metabolically.

Common markers used alongside A1c

Because A1c alone can miss early insulin resistance, clinicians sometimes use additional markers for a fuller picture:

• Fasting insulin — elevated levels can indicate the pancreas is compensating harder than it should need to.
• HOMA-IR — a calculated score combining fasting glucose and fasting insulin, used as a research and clinical estimate of insulin resistance.
• Waist circumference and body composition — central adiposity correlates strongly with insulin resistance risk.

Why this matters

Because insulin resistance often precedes A1c changes by years, lifestyle changes made while A1c still looks "normal" can have outsized preventive value. A normal A1c is reassuring, but it isn't a guarantee that insulin resistance isn't already present, particularly if other risk factors (family history, central weight gain, sedentary patterns) are in play.