Glossary
Inflammation
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 gap is where most of the confusion lives.
What the research found.
Two rheumatoid arthritis databases recorded the first measurement, where a normal CRP means under 10 milligrams per liter. That turned up in 44 percent of one group and 58 percent of the other, and both the sedimentation rate and CRP read normal in 33 and 42 percent. So a normal marker is common in people who have the disease.
For spotting giant cell arteritis, CRP caught 74 percent of the cases and cleared 49 percent of the people who didn't have it. Its area under the curve was 0.675. The sedimentation rate caught 48 percent and cleared 72 percent, so the two split cleanly rather than one beating the other.
The usual age rule for the sedimentation rate takes two forms. For men you take your age and halve it, and for women you add ten to your age first and then halve it. Applying that rule removed an apparent age difference in a group of 263 patients.
One trial gave people an anti-inflammatory diet and a control diet in turn, so each person ate both. Disease activity didn't differ between the two on the test the trial planned in advance. Its P value was 0.116.
Vadell and colleagues, American Journal of Clinical Nutrition, 2020
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 runs 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 stands 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.
How badly the blood tests capture it
Two tests are what people mean when they say measuring inflammation, and those are CRP and the sedimentation rate. Both are useful, and both are worse than their reputation. The clearest proof comes from two databases of consecutive rheumatoid arthritis patients in ordinary care.
Each database recorded the first measurement, where a normal CRP means under 10 milligrams per liter. That turned up in 44 percent of patients in one database and 58 percent in the other, both the sedimentation rate and CRP read normal in 33 and 42 percent, and three tests read normal in 15 and 14 percent. All three read abnormal in only 28 and 23 percent, those three being the sedimentation rate, CRP, and rheumatoid factor.
So about half the people turning up with rheumatoid arthritis had a normal CRP, which makes a normal marker common in active disease. Our record notes one thing about those figures. They come from 1980 to 2004 and used the ordinary CRP test rather than the high-sensitivity one, which affects the thresholds more than it affects the general point.
What raises them besides your disease
A raised marker says inflammation is present and says nothing at all about where in you it came from. That limit is what keeps these tests in a supporting role. Infection raises them, injury raises them, and so does a long list of other conditions that have nothing to do with a rheumatic disease.
The accuracy figures from giant cell arteritis make the problem plain. CRP caught 74 percent of the cases and cleared 49 percent of the people who didn't have it, at an area under the curve of 0.675. Clearing 49 percent leaves 51 percent, so about half the people tested had a raised result anyway without having the disease.
The sedimentation rate has a further problem of its own. It measures how fast red cells settle in a tube, which inflammation affects, and so do your age, low blood counts, and pregnancy. Its usual upper limit is a rule rather than a fixed figure: for men you take your age and halve it, and for women you add ten first and then halve it. Applying that rule removed an apparent age difference in a group of 263 patients.
Why the two markers disagree
CRP is a protein your liver makes when it gets inflammation signals, and it rises and falls within a day or two. The sedimentation rate reflects a physical property of blood instead. That property changes a good deal more slowly than the protein does, and sending both tests is standard, because they catch different parts of one process.
The result is that they often disagree, and a disagreement between them is normal rather than a lab error. In the giant cell arteritis data, CRP caught more cases, at 74 percent against 48 percent, while the sedimentation rate cleared more healthy people, at 72 percent against 49 percent. So neither is the better test, and each covers part of what the other misses.
Reading a trend tells you more than reading one pair of results, and that holds for both tests. It holds most for the sedimentation rate. Because that one moves slowly, two measurements a week apart may say very little, and your team reads them against your symptoms and your exam rather than on their own.
The word as a marketing term
Somewhere between the physiology and the supplement aisle, inflammation stopped being a measurable thing and became a general explanation for feeling unwell. Products and diets get described as anti-inflammatory because a marker moved in a study, which isn't the claim that a disease improved. Separating those two is the single most useful skill for reading in this area.
The trial most often quoted for diet lowering disease activity shows it clearly. Disease activity didn't differ between the anti-inflammatory diet and the control diet on the test the trial planned in advance, at a P value of 0.116. The significant figure people quote comes from a different and unplanned test using only the people who finished both periods, and the paper's title reads as positive.
This picture repeats across the sourced pages here. Trials in these conditions have improved fitness and tiredness, they have moved a fatty acid reading and a cytokine level, and they have left the disease activity scores where they were. So when something is described as reducing inflammation, ask which measurement moved, and then ask whether disease activity was one of them.
What to do with a marker result
A raised result is worth reporting 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 sit 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.
- CRP and ESR, the two tests this word usually refers to in practice.
- DAS28, the composite score that lifestyle studies keep failing to move.
- Rheumatoid arthritis and blood tests, for how often these markers are normal at diagnosis.
- Vasculitis and blood tests, for the accuracy figures in the disease where a normal result is most dangerous.
Questions patients ask.
What is inflammation?
It's the immune system answering an injury or something it treats as a threat. Blood flow to the area rises, immune cells come into the tissue, and you get the swelling, heat, redness, and pain that follow. In autoimmune disease that response is aimed at your own tissue, with no outside threat present at all, which is what separates it from the swelling of a cut or an infection. Both of those settle once the cause is gone.
Do blood tests measure my inflammation?
Partly, and worse than their names suggest. Two rheumatoid arthritis databases recorded the first measurement, where a normal CRP turned up in 44 and 58 percent of patients, and both markers read normal in 33 and 42 percent. So a normal result is common in people with genuinely active disease, which makes these tests better at confirming inflammation than at ruling it out.
What's the difference between CRP and the sedimentation rate?
CRP is a protein your liver makes when it gets inflammation signals, and it moves within a day or two. The sedimentation rate measures how fast red cells settle, which inflammation affects, and so do your age, low blood counts, and pregnancy, and it moves more slowly. Because the two measure different things they often disagree, and that disagreement is normal rather than a lab error.
Why is my sedimentation rate read against my age?
Because the age effect is large enough to matter, so the usual upper limit is a rule rather than a number. For men you take your age and halve it, and for women you add ten first and then halve it, and that rule removed an apparent age difference in a group of 263 patients. The rule comes from population figures rather than an outcome study, so it argues for care about slightly raised results in older people.
What else raises these markers?
Infection, injury, and a long list of other conditions all raise them. That's why a raised marker says inflammation is present rather than what caused it. In giant cell arteritis, CRP cleared only 49 percent of the people who didn't have it, so about half of them still had a raised result without having the disease. That's the reason these tests support an assessment rather than replacing one.
Is an anti-inflammatory diet worth trying?
That depends on what you expect from it, because the trial most often quoted didn't show what it gets quoted for. Disease activity didn't differ between the two diets on the test planned in advance, at a P value of 0.116. Eating well is worth doing for plenty of reasons that have nothing to do with your joints, and expecting a measurable drop in disease activity goes past what these trials found.
How do I judge a claim that something reduces inflammation?
Ask which measurement moved. A marker changing is one claim, a symptom score changing is another, and a disease outcome changing is a third, and the first is far easier to produce than the third. Several trials here improved fitness, tiredness, or a lab value while leaving the disease activity scores unchanged, so a claim about inflammation that names no outcome isn't yet a claim about your disease.
References.
- 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
- 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
- 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
- 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
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.