Fasting Insulin
Definition
The blood insulin level measured after 8 to 12 hours without food, reflecting the baseline insulin output needed to maintain glucose homeostasis. Fasting insulin rises years before fasting glucose becomes abnormal in the progression toward type 2 diabetes, making it one of the earliest detectable markers of insulin resistance. While CGMs do not measure insulin directly, consistently elevated fasting glucose on a CGM (above 100 mg/dL) often correlates with elevated fasting insulin levels.
Why “Fasting Insulin” Matters for Glucose Monitoring
Understanding fasting insulin is essential for anyone using or evaluating a continuous glucose monitor. This concept directly affects how CGM devices are designed, how glucose data is interpreted, and how clinical decisions about blood sugar management are made.
This term applies broadly across all continuous glucose monitors and is foundational knowledge for interpreting CGM data, whether you are managing diabetes or using a sensor for metabolic wellness.
Related Terms
Homeostatic Model Assessment of Insulin Resistance, calculated as fasting insulin (μU/mL) multiplied by fasting glucose (mg/dL) divided by 405.
A metabolic condition in which the body's cells respond poorly to the hormone insulin, forcing the pancreas to produce progressively larger amounts to maintain normal blood glucose levels.
A protein fragment released by the pancreas in a 1:1 ratio with insulin during the conversion of proinsulin to active insulin.
A cluster of 5 interrelated conditions — elevated waist circumference, high triglycerides, low HDL cholesterol, high blood pressure, and high fasting glucose — that together increase the risk of cardiovascular disease by 2x and type 2 diabetes by 5x.