Inflammation markers: what CRP, ESR and a cytokine panel measure

Inflammation markers are the measurable traces of immune activity in the blood. They fall into families:

• Acute-phase proteins such as CRP and serum amyloid A, which the liver produces when inflammatory signals such as IL-6 reach it (Hunter and Jones, 2015).
• Cytokines, the signalling proteins immune cells use to coordinate inflammation, such as IL-6, IL-1β and TNF-α, and regulators such as IL-10 and IL-1Ra (Hunter and Jones, 2015).
• Interferons, such as IFN-α, IFN-β and IFN-γ.
• Chemokines, such as IP-10 and MCP-1.

A standard "inflammatory markers blood test" means CRP, ESR or both. A research or specialist panel reaches into the other families. Our guides to what inflammation markers are and what each marker of inflammation signals walk through them one by one.

Inflammation starts with immune cells that sense a threat, such as an infection or damaged tissue, and release cytokines. Those messengers act at the site and travel through the blood. Some reach the brain and produce the fatigue, malaise and poor concentration of sickness behaviour (Dantzer et al., 2008). IL-6 reaches the liver, which answers by making CRP (Hunter and Jones, 2015).

That chain explains why the markers behave the way they do. CRP rises after the signal that caused it, so it reports that inflammation happened and says little about which pathway drove it. IL-6 itself has effects that spread across many pathways, which is why a review in Nature Immunology called it a keystone cytokine (Hunter and Jones, 2015). Our piece on IL-6, TNF and CRP follows the chain step by step.

A short burst of inflammation resolves. Persistent immune signalling is a focus of research into long COVID, ME/CFS and other chronic illness, and a 2023 Nature study found immune differences between people with long COVID and people who recovered at the group level (Klein et al., 2023). No single cytokine explains any of these conditions, and research reads them as patterns. Our piece on chronic inflammation and chronic illness covers the evidence.

CRP is the inflammation marker most doctors order. A standard CRP test picks up the large rises of infection and active inflammatory disease. The hs-CRP test uses a more sensitive assay to measure low levels, and cardiology has studied it for years as a marker of cardiovascular risk: the 2003 AHA/CDC statement placed below 1, 1 to 3 and above 3 mg/L as low, moderate and high risk (review, 2009). Our hs-CRP test explainer covers what the number means and what it cannot say.

ESR, the erythrocyte sedimentation rate, measures how fast red blood cells settle in a tube. Many proteins affect it, which makes it an indirect measure (review, 2009).

Both tests help doctors, and both leave most immune signalling unmeasured. A normal CRP or ESR says little about interferon activity, chemokine traffic or cytokines that do not run through the IL-6 route. The CDC notes that routine blood tests may be normal in someone with long COVID (CDC), and a large study found common lab tests unreliable for diagnosing it (CU Anschutz).

A cytokine panel measures several signalling proteins from one sample, which keeps the readings comparable and lets a pattern show. Assays now reach low concentrations: a single-molecule immunoassay measured IL-6, TNF-α, IL-10 and IL-1β at concentrations as low as 0.01 to 0.03 pg/mL (2023 assay study). Affinity-based proteomics goes further and quantifies thousands of protein targets in blood (Nature Communications, 2021). An inflammation panel built on these methods places each protein against a healthy reference, and a retest turns a snapshot into a series, which the FDA-NIH BEST glossary calls a monitoring biomarker. Our comparison of an inflammation panel and standard blood work and our guide to cytokine panel testing go into the detail.

The limits are real. No cytokine or panel diagnoses a condition on its own, and a single raised value is a question to take to your doctor. One reading means less than a series. A panel cannot tell you which treatment to try.

Mune Mirror™^* is currently in development, and the performance characteristics of this test have not yet been established. It is investigational. It does not diagnose, detect, screen for, treat, cure or prevent any disease. Results are for research and informational purposes, to discuss with your own doctor.

For collection options, see at-home inflammation testing and how to test for inflammation. The guide to unwellness testing explains how this measurement fits beside standard care.

Mune Mirror™ is a broad inflammation panel: more than 1,000 immune and inflammation proteins from an at-home sample, including IL-6, TNF-α, IL-1β, IFN-γ, IP-10 and CRP, each benchmarked against a healthy reference and repeated over time. It gives you and your doctor the upstream signals a standard CRP or ESR leaves out.

What is the most common inflammatory markers blood test?

CRP is the inflammation marker doctors order most, with ESR alongside it. The hs-CRP test measures low CRP levels, and cardiology uses it for risk assessment. Specialist and research panels add cytokines, interferons and chemokines.

What is the difference between a CRP test and an hs-CRP test?

Both measure C-reactive protein. A standard CRP test picks up the large rises of infection and active inflammation. The hs-CRP test uses a more sensitive assay to measure low levels, which cardiology uses for risk assessment: below 1, 1 to 3 and above 3 mg/L as low, moderate and high risk under a 2003 AHA/CDC statement.

What does a cytokine panel measure?

A cytokine panel measures several of the signalling proteins immune cells use to coordinate inflammation, such as IL-6, TNF-α, IL-1β, IL-10 and IFN-γ, from one sample. The results show a pattern against a reference range. They do not diagnose a condition on their own.

Can inflammation markers be normal when you feel unwell?

Yes. CRP and ESR are downstream and indirect, and they leave most immune signalling unmeasured. The CDC notes that routine blood tests may be normal in someone with long COVID. A normal result makes some causes less likely and does not make symptoms less real.

What is an inflammation panel?

An inflammation panel measures many inflammatory proteins at once, from cytokines and interferons to chemokines and acute-phase proteins, in place of a single CRP value. Broad research-grade panels measure hundreds to more than a thousand proteins against a healthy reference.