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Glossary

Inflammation

The immune response to injury or to a threat the body thinks it sees. In autoimmune disease it's aimed at your own tissue, and a blood test sees only part of it.

Inflammation is the most used and the least exact word in this field. About half the people turning up with rheumatoid arthritis had a normal CRP, so the tests named after it miss a great deal. That difference is where most of the confusion lives.

Quick answerInflammation is the immune response to injury or to a threat, and in autoimmune disease it's aimed at your own tissue. The blood tests are worse than people assume. Two databases recorded the first CRP in rheumatoid arthritis, where a normal one turned up in 44 percent of one group and 58 percent of the other.
The word has drifted a long way from anything you can measure, and products and diets get sold as anti-inflammatory on thin evidence. A marker moved in a study and a disease did not: those are two claims rather than one, because a marker falling isn't the same event as a disease settling. Several trials here show it, having improved fitness, tiredness, or a lab value while leaving the disease activity scores where they were. So when something gets described as reducing inflammation, ask which measurement moved and by how much.

What the word means

Inflammation is the immune system answering an injury, or answering something it treats as a threat. Blood flow to the area rises, immune cells come into the tissue, and the result is swelling, heat, redness, and pain, which anybody knows from a cut or a sprain. That process protects you, and it settles once the cause is gone.

In autoimmune disease the same machinery is active with no outside cause behind it. The response is aimed at your own tissue, and nothing is there to be cleared away, so it doesn't switch off on its own. That's the difference between the swelling of an infection and the swelling of rheumatoid arthritis, and it's why the treatments work by damping the response down rather than by removing a threat.

The word does two other jobs as well. It is in for feeling unwell in general, and it sells things to people who feel unwell. Those three uses of one word are the reason this page exists, and keeping them apart is most of the work of reading anything written about inflammation.

What to do with a marker result

A raised result is worth mentioning and isn't worth reading alone. Infection and injury raise these markers too, so the explanation may have nothing to do with your autoimmune disease at all. Working out which one applies is a clinical judgment that needs the rest of the picture.

A normal result in somebody who feels unwell deserves more attention than it usually gets. About half the people turning up with rheumatoid arthritis had a normal CRP, and in giant cell arteritis a good share of patients had both markers normal, in a disease that threatens sight. So a normal number isn't a reason to stop describing your symptoms.

The best use of these tests is following a trend in somebody whose diagnosis is already settled, which is a different question from diagnosis. A test can be reasonable at one and poor at the other. This site holds no source on how well these markers do for monitoring rather than diagnosis, so this page doesn't claim they're good at it.

Common misconceptions.

Myth. A normal CRP means I don't have active inflammation.

Reality. It doesn't, and the figures are more striking than most people expect. Two rheumatoid arthritis databases recorded the first measurement, where a normal CRP turned up in 44 percent of one group and 58 percent of the other, and both markers read normal in 33 and 42 percent. So about half the people turning up with the disease had a normal CRP, which makes the test a poor gatekeeper.

Myth. The sedimentation rate is a general inflammation meter.

Reality. It measures how fast red cells settle in a tube, and inflammation affects that, and so do your age, low blood counts, and pregnancy. Its upper limit is a rule rather than a fixed number, where for men you take your age and halve it and for women you add ten first and then halve it. So a slightly raised result in an older person may fall inside the limit for their age.

Myth. Something described as anti-inflammatory reduces my disease activity.

Reality. Those are two claims, and only one of them usually gets tested. One trial gave people an anti-inflammatory diet and a control diet in turn, and disease activity didn't differ between them on the test planned in advance, at a P value of 0.116. So when a product or a diet gets described this way, ask which measurement moved, and then ask whether disease activity was one of them.

Myth. If my markers are high the diagnosis is obvious.

Reality. Raised markers say inflammation is present without saying where it came from. In giant cell arteritis, CRP cleared only 49 percent of the people who didn't have it, so about half of them had a raised result anyway. Infection raises these markers, injury raises them, and so do many other conditions, which is why they support a clinical picture rather than pointing at a diagnosis on their own.

Related terms.

References.

  1. Sokka T; Pincus T. Erythrocyte sedimentation rate, C-reactive protein, or rheumatoid factor are normal at presentation in 35%-45% of patients with rheumatoid arthritis seen between 1980 and 2004: analyses from Finland and the United States. The Journal of rheumatology. 2009;36:1387-90. 10.3899/jrheum.080770Retrospective analysis of two consecutive usual-care RA databases
  2. Currier C; Bays A; Thomason J. Normal inflammatory markers in giant cell arteritis: a diagnostic blind spot. Rheumatology International. 2025;45. 10.1007/s00296-025-05930-3Retrospective diagnostic accuracy study within a single fast-track GCA clinic
  3. Ranganath VK; Elashoff DA; Khanna D et al. Age adjustment corrects for apparent differences in erythrocyte sedimentation rate and C-reactive protein values at the onset of seropositive rheumatoid arthritis in younger and older patients. The Journal of rheumatology. 2005;32:1040-2. PMID 15940764Observational cohort analysis of 263 patients with early seropositive RA enrolled within 14 months of symptom onset
  4. Vadell AKE; Bärebring L; Hulander E et al. Anti-inflammatory Diet In Rheumatoid Arthritis (ADIRA)-a randomized, controlled crossover trial indicating effects on disease activity. The American Journal of Clinical Nutrition. 2020;111:1203-1213. 10.1093/ajcn/nqaa019Randomized controlled crossover trial

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This page gathers the published research on this subject into one place. The studies behind it were published between 1989 and 2026, and every figure links to the paper it came from. Those studies were peer reviewed. This summary of them was not. Dr. Sarah Luebker is reviewing these pages one at a time and has not reached this one yet, so it carries no medical review date and nothing here is her opinion or her advice to you. Each page gets updated as she reaches it. It is here in the meantime because the science is worth having in one organized place that is easy to find and easy to read. Talk to your own clinician before acting on any of it.