Finding the right tests…
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Finding the right tests…
Hormonal
Interleukin-6, or IL-6, is a signalling protein your immune system releases during inflammation, infection, and tissue injury. This test measures how much is in your blood. In hospital settings, especially in newborns and critically ill patients, doctors have studied IL-6 as an early marker of serious infection, since it can rise within hours, often faster than more familiar markers like CRP. Even so, IL-6 testing isn't yet a routine, standardised part of everyday outpatient checkups the way CRP is. Its main established clinical use is in specific settings such as suspected sepsis, and its use elsewhere is still mostly in research.
The test measures IL-6 in a blood sample, usually reported in picograms per millilitre (pg/mL). IL-6 rises quickly after an infection or injury starts, sometimes within two to three hours, and can decline again within a day. Because so many things can raise it, from infections to autoimmune conditions to recent surgery or trauma, a single IL-6 value is rarely read on its own. Your doctor will interpret it alongside your symptoms, other blood markers, and your clinical situation.
IL-6 is a cytokine, a small signalling protein, that your immune cells release to coordinate the body's response to infection, injury, or inflammation. It helps trigger fever, prompts the liver to make other markers like CRP, and helps direct immune cells to the site of a problem.
- Research and some hospital settings use IL-6 as an early marker of possible bloodstream infection or sepsis, since it can rise faster than CRP - It has been studied in newborns as part of working out early-onset infection - It's used in some specialised settings to help judge the severity of a person's inflammatory response
Unlike CRP, IL-6 testing hasn't been standardised the same way across labs, and researchers studying it note that agreed cut-off values still differ between studies. That means a raised IL-6 level needs to be read in the context of your symptoms and other tests, rather than treated as a definite answer on its own. It's also raised by a wide range of conditions beyond infection, including autoimmune disease, recent surgery, and even strenuous exercise, which is why it isn't used as a stand-alone screening test in routine outpatient care.
A high IL-6 usually means your body is mounting an inflammatory response, which can be triggered by infection, injury, surgery, or certain autoimmune conditions. Your doctor reads it alongside your symptoms and other tests rather than on its own.
Not typically. IL-6 is mainly used in specific situations, such as investigating suspected serious infection in a hospital setting, rather than as a routine screening test. Ask your doctor whether it's appropriate for your situation.
Both are markers of inflammation, but IL-6 tends to rise earlier, sometimes within hours of an infection starting, while CRP takes longer to increase. Despite this, CRP remains more widely standardised and commonly used in routine practice.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
No special fasting is usually required for this test. Confirm the details with your doctor or the centre when you book.
Reference ranges for IL-6 vary between labs and testing methods more than for many other blood tests, so there isn't one single accepted normal value. Your report will list the range used by that laboratory, and ranges vary by lab, so ask your doctor to explain your specific result.
Yes, intense physical activity, recent surgery, and several non-infectious conditions can all raise IL-6, not just infection. Tell your doctor about anything recent that might affect your result.
No, IL-6 is a general marker of inflammation rather than a test for one specific condition. Your doctor uses it as one piece of information alongside your history, symptoms, and other tests.