Can a rising fasting glucose with normal HbA1c and insulin signal early cardiometabolic risk?

A modest, persistent rise in fasting glucose can be clinically meaningful even when HbA1c and fasting insulin appear optimal, but it is best viewed as a risk marker requiring context and confirmation—not as proof of a defined metabolic sequence.

Clinical and prognostic evidence

• Within conventionally normal fasting-glucose ranges, higher values predict later cardiometabolic outcomes. In adults without baseline cardiovascular disease, fasting glucose 95–99 mg/dL was associated with incident cardiovascular disease versus <80 mg/dL (adjusted HR 1.53).
• Diabetes risk also rises across high-normal values: fasting glucose 91–99 mg/dL carried an adjusted HR of 2.03 versus lower-normal glucose, with graded associations replicated in a Japanese cohort.
• Longitudinal cohorts show fasting glucose and HbA1c both rise before diabetes, with fasting glucose accelerating about 3 years before diagnosis in Whitehall II. This supports an evolving dysglycemic process, but not a reliably established fasting-glucose-first interval while HbA1c remains optimal.

Mechanistic interpretation

• Fasting glucose predominantly reflects hepatic glucose production. Early hepatic insulin resistance and/or reduced beta-cell secretory reserve can therefore shift fasting glucose upward before overt hyperglycemia.
• However, the usual prediabetic trajectory more often begins with declining insulin sensitivity and compensatory hyperinsulinemia. In Whitehall II, insulin sensitivity declined approximately 5 years before diabetes—about 2 years before fasting glucose accelerated. A normal fasting insulin neither excludes insulin resistance nor supports the claim that glucose drift generally precedes insulin abnormality.
• Higher fasting insulin is itself associated with coronary heart disease risk, reinforcing that insulin-related abnormalities may be early relevant signals.

Practical interpretation

• Bottom line: For this 52-year-old man, a reproducible upward fasting-glucose trend merits broader cardiometabolic assessment—waist/weight trajectory, blood pressure, lipids, medications, and lifestyle—despite normal HbA1c and fasting insulin. Repeat standardized testing is important because fasting glucose varies meaningfully day to day; discordant results may warrant repeat testing or an alternative measure such as OGTT.