Systemic Immune-Inflammation Index (SII)
Here’s what it reflects — and what to do about it.
Longetic pulls together every lab and record you’ve had, follows how Systemic Immune-Inflammation Index (SII) changes over time, and explains what’s shifting — so you walk into your next appointment prepared, with reminders for retests along the way.
What is Systemic Immune-Inflammation Index (SII)?
A calculated index combining platelets, neutrophils, and lymphocytes into a single marker of systemic inflammation.
SII is a calculated value from a routine CBC: it multiplies your platelet count by your neutrophil count and divides by your lymphocyte count - (platelets times neutrophils) divided by lymphocytes. A higher SII can be associated with a stronger systemic inflammatory state and, in research, less favorable outcomes, a lower value can be associated with a calmer immune profile. It is a general signal, not a diagnosis.
What to know about Systemic Immune-Inflammation Index (SII)
Understanding Systemic Immune-Inflammation Index (SII) means knowing what it reflects, what tends to move it, and the signs that suggest it’s worth a closer look — so you can bring the right questions to your next appointment.
This glossary entry is for informational purposes only and is not a substitute for professional medical advice. Read our Medical Disclaimer.
References
About our sources
Official sources
Government health agencies, national institutes, and intergovernmental bodies whose guidelines carry regulatory or policy weight.
Clinical / professional
Medical societies, specialty colleges, and professional associations whose consensus statements reflect clinical practice standards.
Peer-reviewed research
Original research articles and systematic reviews published in indexed journals and verified through PubMed or DOI.