Insulin

Insulin is the master hormone of metabolism — produced by beta cells in the pancreas, it’s the key that unlocks your cells to let glucose in. When you eat, blood glucose rises, triggering insulin release. Insulin then signals cells throughout your body to absorb glucose for energy or storage. Without insulin, glucose accumulates in the blood while cells starve.

Why does this matter? Insulin levels reveal what’s happening behind abnormal glucose. High insulin with high glucose indicates insulin resistance — the cells aren’t responding, so the pancreas produces more. Low insulin with high glucose indicates insulin deficiency — the pancreas can’t produce enough. This distinction determines whether you have Type 1 diabetes, Type 2 diabetes, or prediabetes, guiding treatment choices.

Insulin testing isn’t routine for everyone, but it’s invaluable for evaluating insulin resistance, classifying diabetes, investigating hypoglycemia, and understanding metabolic health at a deeper level than glucose alone.

Order Your Metabolic Panel

---

Key Benefits of Testing

Insulin testing uncovers what glucose testing cannot — the underlying mechanism of blood sugar problems. Is the pancreas producing too much insulin (resistance), too little (deficiency), or is something else going on (insulinoma, medication effect)? This guides appropriate treatment.

For those concerned about metabolic health, fasting insulin can detect insulin resistance years before glucose becomes abnormal. Early detection allows intervention when lifestyle changes are most effective.

---

What Does This Test Measure?

Insulin testing measures the concentration of insulin hormone in your blood. Results are interpreted alongside glucose for maximum diagnostic value.

How Insulin Works

Production: Insulin is made by beta cells in the pancreatic islets of Langerhans. When blood glucose rises, beta cells release insulin into the bloodstream.

Action: Insulin binds to receptors on cells throughout the body, triggering glucose transporters to move glucose from blood into cells. It also promotes fat storage, protein synthesis, and inhibits glucose release from the liver.

Clearance: The liver removes much of the insulin from blood on first pass. Insulin has a short half-life — levels change rapidly with meals and fasting.

Insulin and Glucose Together

The relationship between insulin and glucose reveals the underlying problem:

Normal: Glucose rises after eating → Insulin rises → Glucose returns to normal → Insulin returns to baseline

Insulin resistance: Glucose rises → Insulin rises MORE (compensating) → Glucose still elevated → Insulin stays high

Insulin deficiency: Glucose rises → Insulin can’t rise adequately → Glucose stays very high → Insulin low or absent

Fasting vs. Stimulated Insulin

Fasting insulin: Measured after overnight fast. Reflects baseline insulin production and insulin sensitivity. High fasting insulin suggests insulin resistance.

Post-meal or stimulated insulin: Measured after glucose challenge. Shows how pancreas responds to glucose. Used in specific diagnostic evaluations.

---

Why This Test Matters

Detects Insulin Resistance Early

Insulin resistance is the hallmark of Type 2 diabetes and metabolic syndrome. In early stages, the pancreas compensates by producing more insulin, keeping glucose normal. Fasting insulin rises before glucose does — detecting the problem earlier when intervention is most effective.

Distinguishes Diabetes Types

This is crucial for treatment decisions:

Type 1 diabetes: Low or absent insulin. The immune system has destroyed beta cells. Requires insulin therapy from diagnosis.

Type 2 diabetes: High insulin initially (insulin resistance), declining over time. May respond to oral medications that improve insulin sensitivity or stimulate secretion.

LADA (Latent Autoimmune Diabetes in Adults): Can appear like Type 2 but has autoimmune features. Insulin may be low or declining faster than typical Type 2. May need insulin sooner.

Evaluates Hypoglycemia

When blood sugar drops too low, insulin level helps determine why:

Appropriately low insulin during hypoglycemia: Normal response — the body is correctly suppressing insulin

Inappropriately high insulin during hypoglycemia: Suggests insulinoma (insulin-producing tumor), insulin injection, or insulin-releasing medication

Assesses Metabolic Syndrome

High fasting insulin correlates with metabolic syndrome components — central obesity, hypertension, dyslipidemia, and elevated glucose. It’s a marker of metabolic dysfunction.

Monitors Beta Cell Function

In established diabetes, insulin (or C-peptide, which is more accurate) shows remaining pancreatic function, helping predict treatment needs.

---

What Can Affect Your Insulin?

Causes of High Insulin (Hyperinsulinemia)

Insulin resistance:

• Type 2 diabetes and prediabetes (early stages)
• Metabolic syndrome
• Obesity, especially central/abdominal
• Polycystic ovary syndrome (PCOS)
• Non-alcoholic fatty liver disease

Insulinoma:

• Rare insulin-producing pancreatic tumor
• Causes inappropriately high insulin with hypoglycemia

Exogenous insulin:

• Insulin injections (therapeutic or factitious)
• Note: Exogenous insulin elevates insulin but suppresses C-peptide

Medications:

• Sulfonylureas stimulate insulin secretion

Other:

• Cushing’s syndrome
• Acromegaly
• Stress and acute illness (transient)

Causes of Low Insulin (Hypoinsulinemia)

Type 1 diabetes:

• Autoimmune destruction of beta cells
• Little to no insulin production

Advanced Type 2 diabetes:

• Beta cell exhaustion after years of overproduction
• Eventually may need insulin therapy

LADA:

• Slowly progressive autoimmune diabetes
• Insulin declines over months to years

Pancreatitis or pancreatic damage:

• Chronic pancreatitis
• Pancreatic surgery
• Cystic fibrosis

Normal fasting:

• Insulin is appropriately low after prolonged fasting

Testing Considerations

Fasting required: For most evaluations, 8-12 hours fasting provides consistent baseline. Recent food dramatically affects insulin levels.

Sample handling: Insulin degrades if samples aren’t handled properly.

Medications: Many diabetes medications affect insulin levels. Note all medications when interpreting results.

Interpret with glucose: Insulin alone is less meaningful than insulin in context of corresponding glucose.

---

When Should You Get Tested?

Suspected Insulin Resistance

Features suggesting insulin resistance include central obesity, skin changes (acanthosis nigricans — dark, velvety patches), PCOS, or fatty liver. Fasting insulin helps confirm and quantify resistance.

Classifying Diabetes Type

When diabetes is newly diagnosed, especially in adults where type may be unclear, insulin and C-peptide help distinguish Type 1, Type 2, and LADA — guiding treatment choice.

Evaluating Hypoglycemia

Recurrent low blood sugar episodes, especially in non-diabetics, require insulin measurement during hypoglycemia to determine the cause.

PCOS Evaluation

Insulin resistance is common in polycystic ovary syndrome. Fasting insulin helps assess metabolic status and may guide treatment (metformin).

Metabolic Health Assessment

For comprehensive metabolic evaluation, especially with family history of diabetes or metabolic syndrome, fasting insulin provides earlier insight than glucose alone.

Monitoring Beta Cell Function

In established diabetes, periodic assessment (usually with C-peptide) tracks remaining pancreatic function.

Order Your Test

---

Understanding Your Results

Insulin is always interpreted in context — particularly with simultaneous glucose:

Fasting Insulin Patterns

Normal fasting insulin with normal glucose: Normal insulin sensitivity. Pancreas and cells communicating well.

High fasting insulin with normal glucose: Insulin resistance with compensation. The pancreas is working harder to maintain normal glucose. Early warning sign — lifestyle intervention indicated.

High fasting insulin with high glucose: Insulin resistance — the pancreas can’t keep up anymore. Type 2 diabetes or advanced prediabetes.

Low fasting insulin with high glucose: Insulin deficiency. Suggests Type 1 diabetes, LADA, or advanced Type 2 with beta cell failure. Likely needs insulin therapy.

Low fasting insulin with normal glucose: Usually normal — insulin is appropriately low when glucose is controlled. May also be seen in very insulin-sensitive individuals.

HOMA-IR: Quantifying Insulin Resistance

HOMA-IR (Homeostatic Model Assessment for Insulin Resistance) is calculated from fasting glucose and fasting insulin. It provides a standardized measure of insulin resistance — higher values indicate greater resistance. Many labs calculate and report this automatically.

Insulin During Hypoglycemia

Low insulin during hypoglycemia: Appropriate — the body correctly suppressed insulin when glucose dropped.

High insulin during hypoglycemia: Inappropriate — suggests insulinoma, exogenous insulin, or insulin-releasing medication. Requires further investigation.

---

What to Do About Abnormal Results

For High Insulin (Insulin Resistance)

Lifestyle intervention (most important!):

• Weight loss — especially central/abdominal fat
• Exercise — both aerobic and resistance training improve insulin sensitivity
• Dietary changes — reduce refined carbohydrates, increase fiber, consider lower-carb approaches
• Adequate sleep — poor sleep worsens insulin resistance
• Stress management — chronic stress elevates cortisol and glucose

Medical evaluation:

• Screen for metabolic syndrome components
• Check for PCOS if applicable
• Evaluate liver (fatty liver common with insulin resistance)

Medications if indicated:

• Metformin improves insulin sensitivity
• May be considered for high-risk prediabetes

For Low Insulin (Insulin Deficiency)

Confirm diabetes type:

• Check C-peptide (more accurate for endogenous insulin)
• Test diabetes autoantibodies (GAD, IA-2, ZnT8) if Type 1 or LADA suspected

Initiate appropriate treatment:

• Type 1 diabetes: Insulin therapy essential from diagnosis
• LADA: May need insulin sooner than typical Type 2
• Advanced Type 2: Insulin often eventually needed

For Hypoglycemia with High Insulin

Investigate cause:

• Review medications — sulfonylureas, insulin
• Check C-peptide — high suggests endogenous source (insulinoma); low suggests exogenous insulin
• Imaging studies if insulinoma suspected

---

Related Health Conditions

Insulin Resistance and Metabolic Syndrome

The Core Defect: Cells don’t respond well to insulin, requiring the pancreas to produce more. Central to Type 2 diabetes, metabolic syndrome, PCOS, and fatty liver. Highly responsive to lifestyle intervention.

Type 2 Diabetes

Insulin Resistance + Declining Production: Starts with insulin resistance and compensatory hyperinsulinemia. Over time, beta cells can’t keep up, insulin production falls, and glucose rises.

Type 1 Diabetes

Absolute Insulin Deficiency: Autoimmune destruction of beta cells eliminates insulin production. Requires lifelong insulin therapy. Insulin and C-peptide are very low or undetectable.

PCOS (Polycystic Ovary Syndrome)

Strong Link to Insulin Resistance: Many women with PCOS have insulin resistance and hyperinsulinemia. High insulin may drive androgen production worsening PCOS symptoms. Metformin may help.

Insulinoma

Insulin-Producing Tumor: Rare pancreatic tumor causing hypoglycemia with inappropriately elevated insulin. Diagnosed by high insulin and C-peptide during hypoglycemia. Usually curable with surgery.

Non-Alcoholic Fatty Liver Disease (NAFLD)

Hepatic Manifestation of Insulin Resistance: Insulin resistance promotes fat accumulation in the liver. High insulin often accompanies fatty liver. Weight loss improves both.

---

Why Regular Testing Matters

For those with risk factors, fasting insulin can detect insulin resistance before glucose becomes abnormal — the earliest stage when lifestyle intervention is most powerful. Tracking insulin over time shows whether interventions are working.

In diabetes management, understanding insulin status guides treatment — whether to use insulin sensitizers, insulin secretagogues, or insulin itself.

---

Related Biomarkers Often Tested Together

Glucose — Essential to interpret alongside insulin. The glucose-insulin relationship reveals the mechanism.

C-Peptide — Measures endogenous insulin production more accurately than insulin (not affected by exogenous insulin).

HbA1c — Long-term glucose control. Complements insulin and glucose for diabetes assessment.

Lipid Panel — Dyslipidemia often accompanies insulin resistance.

ALT — Screen for fatty liver, which commonly accompanies insulin resistance.

HOMA-IR — Calculated index quantifying insulin resistance from fasting glucose and insulin.

Note: Information provided in this article is for educational purposes and doesn’t replace personalized medical advice.