Marker Name: Insulin
REFERENCE RANGES FOR INSULIN:
Laboratory reference range: 2.6-24.9 uIU/ml (fasting serum insulin)
Functional reference range: 2-7 uIU/ml (fasting)
DESCRIPTION:
Insulin is a peptide hormone produced by the β-cells of the pancreatic islets in response to elevated blood glucose levels.1 Its primary role is to facilitate the uptake of glucose into insulin-sensitive tissues—primarily muscle, adipose, and liver—thereby reducing circulating glucose concentrations.2 Insulin also plays a critical role in lipid metabolism by promoting lipogenesis and inhibiting lipolysis, and in protein metabolism by stimulating amino acid uptake and protein synthesis.3
Insulin is secreted in a pulsatile fashion, with basal secretion during fasting and augmented secretion postprandially.4 Upon binding to its receptor, insulin initiates a signaling cascade that involves activation of the insulin receptor substrate (IRS) proteins and the phosphatidylinositol-3-kinase (PI3K)/Akt pathway, resulting in increased translocation of glucose transporter type 4 (GLUT4) to the cell membrane.5
Insulin resistance—a state in which peripheral tissues exhibit decreased responsiveness to insulin—is a hallmark of metabolic syndrome and type 2 diabetes mellitus (T2DM).6 In such states, hyperinsulinemia often compensates for reduced insulin sensitivity, particularly in the early stages. Chronic hyperinsulinemia may contribute to systemic inflammation, endothelial dysfunction, and dyslipidemia.7 Over time, pancreatic β-cell function may decline, leading to inadequate insulin secretion and overt hyperglycemia.8
PATHOLOGICAL/CONVENTIONAL RANGE INDICATIONS:
High in:
Hyperinsulinemia
Insulin resistance (e.g., metabolic syndrome, prediabetes, early type 2 diabetes)
Obesity
Polycystic ovary syndrome (PCOS)
Insulinoma
Cushing’s syndrome
Postprandial states
Exogenous insulin administration (in patients with diabetes)
Low in:
Type 1 diabetes mellitus
Late-stage type 2 diabetes mellitus (β-cell failure)
Pancreatic insufficiency or destruction (e.g., pancreatitis, pancreatectomy)
Advanced autoimmune diseases affecting pancreatic islets
FUNCTIONAL RANGE INDICATIONS:
High in:
Early insulin resistance
Preclinical metabolic syndrome
PCOS (even in lean women)
Compensatory response to high-carbohydrate diets
Chronic stress (due to elevated cortisol impacting insulin sensitivity)
Low in:
Subclinical β-cell dysfunction
Post-infection or autoimmune β-cell compromise
Inadequate protein intake affecting pancreatic function
Advanced burnout of pancreatic β-cells in T2DM
References:
https://www.ncbi.nlm.nih.gov/books/NBK279061/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7285043/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8249576/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3107982/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6953066/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7173673/
https://diabetesjournals.org/diabetes/article/66/7/1755/39908/Insulin-Resistance-and-Inflammation-in