What is the Systemic Immune-Inflammation Index for coronary heart disease?

The Systemic Immune-Inflammation Index (SII) is a blood test that measures inflammation in your body. It is calculated from three types of cells in your blood: platelets, neutrophils, and lymphocytes. The formula is (platelets × neutrophils) / lymphocytes. Doctors use SII to help assess your risk of coronary heart disease (CHD) and how severe it might be. Research shows that higher SII levels are linked to a higher chance of having CHD, especially in people with diabetes or during acute heart events.

What the research says

A review of studies explains that SII is a useful marker for CHD because it combines information about blood clotting, inflammation, and immune response ³. It works best for acute coronary syndrome (like heart attacks) and is less useful for long-term stable disease ³. A large study from the National Health and Nutrition Examination Survey (NHANES) found that higher SII levels were associated with a higher chance of having CHD, and this link was different for men and women ¹⁰. Another study in people with both CHD and diabetes found that those with diabetes had higher SII levels than those with CHD alone, and higher SII was linked to more severe blockages in the heart arteries ¹¹. A separate study in people with asthma also found that higher SII was linked to a higher risk of stroke, which is related to heart disease ⁹. Overall, SII appears to be a helpful tool, but it is not perfect and should be used along with other tests.

What to ask your doctor

• What is my SII level and what does it mean for my heart health?
• Should I have my SII checked regularly if I have coronary heart disease or diabetes?
• How does my SII result compare to other inflammation markers like CRP?
• Can lifestyle changes or medications help lower my SII level?
• Is SII more useful for predicting acute heart events or long-term risk?