Fasting Glucose
Fasting Plasma Glucose
What it is
Fasting plasma glucose measures the concentration of glucose in the blood after a minimum eight-hour fast — the state in which hepatic glucose output (gluconeogenesis and glycogenolysis) is the primary determinant of circulating glucose, rather than recent dietary intake. In a metabolically healthy individual, overnight fasting glucose is tightly regulated within a narrow range by the coordinated action of insulin and glucagon. Insulin suppresses hepatic glucose output; glucagon stimulates it when glucose falls. Fasting glucose rises when insulin signalling is impaired — either because the pancreas cannot produce sufficient insulin (type 1 diabetes, late type 2 diabetes), because peripheral and hepatic tissues are resistant to insulin's effect (insulin resistance, early type 2 diabetes), or both. Fasting glucose is the simplest and most widely used clinical measure of glycaemic status, and forms the backbone of diabetes diagnostic criteria alongside HbA1c and the oral glucose tolerance test.
Why we measure it
Fasting glucose sits in a diagnostic triad with HbA1c and fasting insulin, each measuring a different dimension of glycaemic health. HbA1c captures the three-month average of glucose exposure — a slow-moving signal that reflects sustained glycaemic burden. Fasting insulin is the earliest signal of insulin resistance, rising years before glucose does. Fasting glucose occupies the middle ground: it reflects the current glycaemic state rather than the three-month average, and it is the value that crosses clinical diagnostic thresholds. A person can have elevated fasting insulin and normal fasting glucose for years — the pancreas is compensating. When fasting glucose begins to rise into the impaired fasting glucose (IFG) range, compensation is beginning to fail. Tracking fasting glucose quarterly alongside insulin and HbA1c allows the protocol to detect this transition and map the direction of travel — whether the metabolic trajectory is improving, stable, or drifting toward frank hyperglycaemia. The ADA diagnostic classification (normal, IFG, diabetes) provides the reference framework; the trend across draws provides the clinical signal.
Why every 3 months
Fasting glucose responds to changes in dietary composition, body weight, physical activity, sleep quality, and medications on a timescale of days to weeks — meaningfully faster than HbA1c, which takes three months to fully reflect a change. This responsiveness makes quarterly measurement valuable: a dietary intervention, a weight loss programme, or a change in physical activity will be visible in fasting glucose within weeks, providing useful feedback long before HbA1c catches up. It also means that fasting glucose is more sensitive to short-term perturbations — a period of acute stress, poor sleep, or illness will transiently elevate it — making the trend across multiple quarterly draws more informative than any single reading.
What movement means
The American Diabetes Association (ADA) and World Health Organisation (WHO) classify fasting plasma glucose into three bands. These are diagnostic thresholds defined by external bodies — not targets set by Nexuses. What the protocol provides is the trend: whether fasting glucose is stable within a band, moving between bands, or drifting within the normal range in a direction that warrants attention even before crossing a threshold.
Normal
< 5.6 mmol/L (< 100 mg/dL)
Within the ADA-defined normal fasting glucose range. The trend within this range is informative — a reading that has risen from 4.2 to 5.4 mmol/L over two years, while still technically normal, represents a meaningful metabolic shift worth investigating alongside fasting insulin and HbA1c.
American Diabetes Association Standards of Medical Care in Diabetes, 2024
Impaired Fasting Glucose
5.6 – 6.9 mmol/L (100 – 125 mg/dL)
Prediabetes by ADA criteria. Indicates impaired glucose regulation and substantially elevated risk of progressing to type 2 diabetes. Also associated with elevated cardiovascular risk independent of diabetes status. Highly responsive to lifestyle intervention — dietary change, weight loss, and exercise are effective at reversing IFG.
American Diabetes Association Standards of Medical Care in Diabetes, 2024
Diabetes
≥ 7.0 mmol/L (≥ 126 mg/dL) on two separate occasions
Diagnostic threshold for type 2 diabetes by ADA/WHO criteria (requires confirmation on a second draw). Clinical review and specialist management are indicated.
WHO Diabetes Diagnostic Criteria, 2011; ADA Standards of Medical Care in Diabetes, 2024
In the protocol
References
- 1.
American Diabetes Association. “Standards of Medical Care in Diabetes — 2024.” Diabetes Care. 2024.
- 2.
World Health Organization. “Use of Glycated Haemoglobin (HbA1c) in the Diagnosis of Diabetes Mellitus.” WHO Report. 2011.
- 3.
Tabák AG, Herder C, Rathmann W, Brunner EJ, Kivimäki M. “Prediabetes: A High-Risk State for Diabetes Development.” The Lancet. 2012.
- 4.
Knowler WC, Barrett-Connor E, Fowler SE, et al.. “Reduction in the Incidence of Type 2 Diabetes with Lifestyle Intervention or Metformin.” New England Journal of Medicine. 2002.