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Immune defense

Systemic Immune-Inflammation Index

Also known as: SII, Immune-Inflammation Index, Systemic Inflammatory Index

The Systemic Immune-Inflammation Index (SII) is a blood-based calculation that reflects the balance between your body’s immune defense and inflammation.

It uses three values from a standard complete blood count (CBC): platelet count, neutrophil count, and lymphocyte count. 

The formula is SII = (Platelets × Neutrophils) ÷ Lymphocytes.

SII has gained attention in research as a marker that integrates both the inflammatory and immune components of blood. It’s being studied as a potential indicator of outlook in cancers, cardiovascular disease, and metabolic disorders — conditions where chronic inflammation plays a role.

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Key takeaways

  • Sample required: Blood

  • Tests for: A combined measure of immune and inflammatory activity, calculated from platelet, neutrophil, and lymphocyte counts

  • Healthy range: Varies by population and lab, but generally lower SII values reflect balanced immune activity

What can an SII test tell you?

The SII test provides insight into the interaction between inflammation and immune function. High values may reflect active inflammation or immune dysregulation, while low values may suggest suppressed immune activity or balanced inflammation control.

Providers or researchers may use SII to:

  • Assess systemic inflammation in chronic diseases (like cardiovascular or autoimmune conditions)

  • Evaluate immune status in people with cancer, infections, or metabolic disorders

  • Monitor response to treatments that influence immunity or inflammation

  • Investigate risk or prognosis in people with elevated inflammatory markers

While SII is not a diagnostic test, it’s considered a promising indicator of how well your body is managing immune activation and inflammation together.

What is being tested?

SII doesn’t measure one specific substance — it combines data already available from a complete blood count (CBC):

  • Neutrophils increase during infection or inflammation

  • Lymphocytes reflect immune regulation and defense

  • Platelets contribute to inflammation and clot formation

By combining these values, SII provides a snapshot of the balance between immune activity and inflammation, helping inform researchers and clinicians about chronic disease patterns and treatment responses.

Where is the SII test typically included?

SII is not yet a routine lab test, but it can be calculated from a standard CBC. It’s commonly used in research or specialized clinical settings to study:

  • Oncology (solid tumors, hematologic cancers)

  • Cardiovascular disease

  • Metabolic or autoimmune disorders

  • Infection-related inflammation

Who should get an SII test?

SII may be used in specific contexts where inflammation or an immune imbalance is suspected.

A provider or researcher may consider this calculation for individuals who:

  • Have chronic inflammatory or autoimmune diseases

  • Are undergoing cancer evaluation or treatment

  • Show persistent elevated CRP, ESR, or white blood cell abnormalities

  • Have metabolic or cardiovascular disease risk factors

It may also be used as a research or monitoring tool in public health and clinical studies.

How Labs by Hers works

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  • 2

    Get your results

    Review your lab results to understand which areas of your health may need attention.

  • 3

    Spot early signals

    Identify potential health risks or system imbalances before they become more serious.

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    Receive expert guidance tailored to your health profile and test results.

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    Track your progress through a mid-year panel and ongoing provider check-ins.

Not available in all 50 states. Eligibility and provider order required. Lab results alone are not intended to diagnose, treat, or cure any condition. A provider will reach out about critical results and plans include access to 24/7 provider messaging.

Images for illustrative purposes only.

Frequently asked questions

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What can cause changes in the SII?

SII can increase with inflammation, infection, stress, cancer, or metabolic disorders. It may decrease when inflammation resolves or with immunosuppressive treatment.

What is a healthy SII range?

This number varies by population and lab, but generally, lower SII values reflect balanced immune activity.

Is the SII test part of a standard blood panel?

No, but it can be calculated from values in a complete blood count (CBC) that you may have already done.

Why is the SII being studied?

Researchers study SII because it may help predict outcomes in heart disease, cancer, and chronic inflammatory conditions where immune activity plays a role.

Can lifestyle affect SII?

Yes. Diet, smoking, exercise, stress, and sleep quality can all influence inflammation and immune activity, which affect SII.

Is SII used for diagnosis?

No. It’s a supportive or investigational biomarker, interpreted alongside other clinical findings and tests.

Can I get this test through telehealth?

Yes. Because SII is calculated from a standard CBC, a provider can order labs remotely and review results virtually.

Does insurance cover this test?

Coverage depends on context; while SII itself is not billed separately, the CBC it’s derived from is typically covered as part of general health screening. However, insurance is not required for lab testing through Hers.

What tests are related to this biomarker?

• Complete blood count (CBC)

• C-reactive protein (CRP)

• Erythrocyte sedimentation rate (ESR)

• Neutrophil-to-lymphocyte ratio (NLR)

• Platelet-to-lymphocyte ratio (PLR)

• Interleukin and cytokine panels

The information provided here is for informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always talk to a qualified healthcare provider about your specific health concerns.

Related biomarkers

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Basophils (absolute count)

Basophils are a type of white blood cell that help your body respond to allergens and fight certain parasites.

Learn more about Basophils (absolute count)

Basophils (percentage)

Basophils typically make up less than 1% of your total white blood cells and help trigger allergic responses and fight certain parasites. A healthy percentage means your blood contains the expected proportion of basophils, which are important for normal immune function.

Learn more about Basophils (percentage)

Eosinophils (absolute count)

Eosinophils are a type of white blood cell that help to control allergy-related inflammation and protect against certain parasites. A healthy count means your blood contains the expected number of eosinophils, which are important for normal immune function.

Learn more about Eosinophils (absolute count)

Eosinophils (percentage)

Eosinophils normally make up about 1-4% of your total white blood cells and help your body fight parasites and control allergy-related inflammation. A healthy percentage means your blood contains the expected proportion of eosinophils, which are important for normal immune function.

Learn more about Eosinophils (percentage)

Lymphocytes (absolute count)

Lymphocytes are a type of white blood cell that play a key role in building long-term immunity by recognizing and attacking viruses. A healthy count means your immune system is equipped to defend against infections and maintain balance.

Learn more about Lymphocytes (absolute count)

Lymphocytes (percentage)

Lymphocytes typically make up 20-40% of your total white blood cells and help your body fight viral infections while building long-term immunity. A healthy percentage means your blood contains the expected proportion of lymphocytes, which are important for normal immune function.

Learn more about Lymphocytes (percentage)

Monocytes (absolute count)

Monocytes are a type of white blood cell that help your body defend against bacteria and clean up damaged cells. A healthy count means your immune system is working efficiently to support your healing and protect against infection.

Learn more about Monocytes (absolute count)

Monocytes (percentage)

Monocytes typically make up about 2-8% of your total white blood cells. They act as your body’s clean-up crew to remove damaged cells and help fight bacterial infections. A healthy percentage means your blood contains the expected proportion of monocytes, which are important for normal immune function.

Learn more about Monocytes (percentage)

Neutrophils (absolute count)

Neutrophils are the most common type of white blood cell and act as your body’s first line of defense against bacterial infections. A healthy count means your immune system is well-prepared to respond quickly to infection when needed.

Learn more about Neutrophils (absolute count)

Neutrophils (percentage)

Neutrophils are the most common type of white blood cell, typically making up 50–70% of your total white blood cells. They act as your body’s first line of defense against bacterial infections. A healthy percentage means your blood contains the expected proportion of neutrophils, which are important for normal immune function.

Learn more about Neutrophils (percentage)

White Blood Cell Count

White blood cells are an essential part of your immune system, helping your body fight infections and support healing. A healthy count means your immune defenses are strong and ready to respond in case infection arises.

Learn more about White Blood Cell Count

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Reviewed by Lynn Marie Morski, MD

Published 12/04/2025