Interleukin-6 (IL-6): reference ranges

Q: How does IL-6 differ from CRP?

IL-6 is the signal that triggers CRP production in the liver. It rises earlier, but CRP is cheaper and better standardized.

Q: Why is the test rarely ordered?

Methods are not standardized between laboratories, and CRP plus procalcitonin covers most needs.

Q: Does stress or exercise raise it?

Yes — physical exertion and stress temporarily elevate the level, which is considered in interpretation.

In shortIL-6 is an immune signaling molecule that rises rapidly in infection, injury, and autoimmune disease. In healthy adults it is usually below 5–10 ng/L (same as pg/mL), but references vary widely by method. In routine practice it complements CRP and procalcitonin.

Reference ranges

Group	Reference range
Healthy adults (approximate) — typical range (international reference, not a national standard)	usually < 5–10 ng/L (same as pg/mL); references are strongly method-dependent

No single international reference exists: meta-analyses in healthy adults find medians near 5 ng/L (pg/mL) with wide spread. Only the report's own reference applies. Reference ranges vary between laboratories and assays — use the range printed on your own lab report.

Check your value

Enter your result — we will show how it compares with a typical range. Match the units of the selected row.

Approximate comparison with a typical range, not a diagnosis. Reference intervals vary by laboratory and method — check your report; result interpretation is done by a doctor.

What this marker is

IL-6 triggers the liver's acute-phase response — including CRP synthesis — and drives fever. Its level rises early in bacterial infection and stays elevated in chronic inflammation.

Because assays are not standardized, the test is reserved for complex situations: assessing cytokine responses, rheumatic disease activity, and research settings.

When it is high

Infection and sepsisA marked rise accompanies bacterial infections; the trend helps gauge severity.

Autoimmune diseaseIn rheumatoid arthritis and other systemic diseases IL-6 sustains chronic inflammation.

CancerSome tumors produce IL-6; the level correlates with disease activity.

When it is low

Not clinically meaningfulLow IL-6 is the normal state outside inflammation.

What can skew the result

These factors can shift the value without any disease — worth considering before a retest:

Time of dayPhysical exerciseAcute infection and stress

How to prepare

Morning fasting sample; the level has daily fluctuations, so serial tests are drawn at the same time of day.

When a retest makes sense

Trends are assessed by clinical need, with samples taken at the same time of day.

Who usually reviews this result

A result outside the reference range is usually reviewed by: your GP or primary care doctor; a rheumatologist or infectious disease specialist as appropriate. Bring your lab report and any previous results to the appointment.

Names used on lab reports

Your report may use any of these names:
Interleukin-6IL-6

Units and conversion

Measured in: ng/L

ng/L = pg/mL

1 ng/L = 1 pg/mL — the number stays the same. Results are rounded to 2 decimal places.

Several markers on your report?

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Frequently asked questions

How does IL-6 differ from CRP?