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Insulin (Fasting)

Diabetes Biomarker

Sample Needed

Collection Type: Blood

Body System

Related System: Diabetes

Overview

Fasting insulin measures the concentration of insulin in the blood after an overnight fast and reflects pancreatic beta‑cell secretion of endogenous insulin. The test helps assess how much insulin the body produces at baseline and is used alongside fasting glucose and HbA1c to evaluate insulin resistance, prediabetes, type 2 diabetes risk, metabolic syndrome, and conditions like polycystic ovary syndrome (PCOS). Symptoms prompting testing include excessive thirst, frequent urination, unexplained weight change, fatigue, and skin changes such as acanthosis nigricans. Results vary with age, puberty, pregnancy, body mass index and ethnicity—adolescents, pregnant people and individuals with obesity commonly have higher fasting insulin, while longstanding type 1 diabetes or advanced beta‑cell failure can show low levels.

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Test Preparation

Overnight fasting (8-12 hrs) is required
Do not eat or drink anything except water before the test

Why Do I Need This Test

Profile: Diabetes (metabolic) evaluation - Symptoms: polyuria, polydipsia, unexplained weight change, fatigue, acanthosis nigricans - Diagnoses/monitoring: insulin resistance, early/preclinical type 2 diabetes risk, metabolic syndrome, PCOS; complements glucose/HbA1c testing - Reasons for abnormal levels: insulin resistance or hypersecretion (high); beta‑cell failure, autoimmune diabetes or pancreatitis (low) - Biological meaning: high insulin indicates compensatory response to insulin resistance; low insulin indicates inadequate insulin production - Lifestyle causes: obesity, high‑calorie/high‑carb diet, physical inactivity, certain medications - Family history: first‑degree relatives with type 2 diabetes, metabolic syndrome or PCOS increases likelihood of abnormal results

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Understanding Test Results

Values less than ~2 µIU/mL suggest low endogenous insulin secretion and may reflect beta‑cell failure as seen in type 1 diabetes, late‑stage type 2 diabetes, chronic pancreatitis, or after pancreatectomy; correlate with low C‑peptide to confirm.
Values within 2–20 µIU/mL are generally considered normal fasting insulin.
Fasting insulin persistently above ~20 µIU/mL indicates hyperinsulinemia and often insulin resistance; levels in the 20–50 µIU/mL range suggest moderate insulin resistance and increased risk for prediabetes, metabolic syndrome, and cardiovascular risk.
Values above ~50 µIU/mL represent marked hyperinsulinemia seen with severe insulin resistance (e.g., severe obesity, lipodystrophy, some endocrine disorders) and warrant evaluation for causes and complications.
Interpret in context of fasting glucose, HbA1c, clinical signs, medications, and consider C‑peptide to distinguish endogenous from exogenous insulin.

Normal Range

2-20 µIU/mL OR 12-120 pmol/L

FAQs

Q: What is insulin fasting?

A: Insulin fasting is a short-term strategy to lower circulating insulin by avoiding calories or carbohydrate-rich, insulin-triggering foods for set periods (often using intermittent fasting windows). The aim is improved insulin sensitivity, reduced fat storage and better metabolic health. It’s not a substitute for medical diabetes care; people with diabetes, on insulin or prone to hypoglycemia should only try it under clinician supervision.

Q: What is the normal insulin level with fasting?

A: A typical fasting insulin level in adults is about 2–20 μIU/mL (14–138 pmol/L). Levels below or above this range may indicate inadequate insulin production or insulin resistance/hyperinsulinemia. Reference ranges vary by laboratory and assay; results depend on fasting duration (usually 8–12 hours), medications, body weight, and health conditions. Discuss abnormal values with your healthcare provider.

Q: Is high fasting insulin bad?

A: High fasting insulin is harmful: it typically indicates insulin resistance and raises risk of type 2 diabetes, cardiovascular disease, fatty liver and metabolic syndrome. It often precedes raised blood sugar. Management includes weight loss, regular exercise, reducing refined carbohydrates, and medical review; medications may be needed if lifestyle changes are insufficient.

Q: How to control fasting blood sugar during pregnancy?

A: Control fasting blood sugar in pregnancy by testing regularly (fasting and postprandial), eating balanced, lower‑GI carbohydrates spread across small, frequent meals, and including protein, healthy fats and a bedtime snack to prevent overnight dips. Stay active with daily walking, maintain healthy weight, avoid sugary foods, manage stress and sleep, follow prenatal appointments, and start medication or insulin if lifestyle measures don’t meet targets.

Q: How to reduce insulin fasting?

A: To lower fasting insulin: reduce refined carbs and added sugars, choose high-fiber, low-glycemic foods and healthy fats; lose excess weight; do regular aerobic and resistance exercise; try time-restricted eating or intermittent fasting under medical guidance; improve sleep and manage stress; avoid smoking and excess alcohol; and follow prescribed medications or medical advice when needed.

Q: How to check your fasting insulin levels?

A: To check fasting insulin, ask your clinician for a fasting insulin blood test. After an 8–12 hour overnight fast, go to a lab (usually in the morning) for a venous blood draw. The lab reports insulin in µIU/mL or pmol/L; your clinician may calculate HOMA‑IR or order additional glucose testing to assess insulin resistance and recommend follow-up if results are abnormal.