In depth
Adult-onset Still's: common questions
Ferritin is the test everybody links to this disease, and on its own it catches about 60 percent of the cases. A second ferritin test alongside it does more. Neither of them settles the diagnosis by itself, and sorting out what each one is worth is what this page does.
What the research found.
Glycosylated ferritin caught 74 percent of Still's disease cases and cleared 80.5 percent of the people who did not have the disease. Plain ferritin caught 60.4 percent and cleared 85.7 percent. So the second test catches more of the cases while clearing slightly fewer of the people who are well.
One rule pairs a glycosylated ferritin of 20 percent or less with a ferritin above the top of normal. That rule caught 70.5 percent of cases and cleared 83.2 percent. Asking instead for five times normal ferritin caught 43.2 percent and cleared 92.9 percent, which is a worse trade.
A ferritin cut-off of 3,500 micrograms per liter helps spot a complication called macrophage activation syndrome, and it works in one direction. It caught 85 percent of the people who had it. When it read below the cut-off, it was right 97 percent of the time, which is where its value sits.
Somebody searched the full text of the 2024 European guideline for Still's disease for four words, which were exercise, physical activity, rehabilitation, and physiotherapy. Not one of the four appears in it. The guideline covers the diagnosis, two classes of drug, short steroid courses, and watching for complications instead.
Fautrel and colleagues, Annals of the Rheumatic Diseases, 2024
People with adult-onset Still's disease scored worse on quality of life than healthy controls did. That held even when their illness showed little or no sign of being active at the time. The physical parts of the SF-36, a general patient-reported quality-of-life questionnaire, dropped most, and disability, tiredness, pain, and general health were all worse too.
What the blood tests are worth
Ferritin is the test people link to adult-onset Still's disease, and the link is earned. Levels in this illness often run far above what other swelling diseases produce. What any one result is worth as evidence is a separate question, and it is the one this section answers.
Pooled across the studies, ferritin caught 60.4 percent of cases and cleared 85.7 percent of the people who did not have the disease. Two other measures of how well it does came out at 0.778 and 11.32. Read in plain terms, that means roughly two in five people with the disease have a ferritin that never flags. About one in seven people without it test positive anyway, and ferritin also rises in infection, in cancer, in liver disease, and when the body holds too much iron.
A second ferritin test adds something to that. Some of the ferritin in your blood has sugar groups attached to it, and this test measures what share of it does, so the result comes back as a percentage. In this illness that share falls rather than rises. It caught 74 percent of cases against ferritin's 60.4, and cleared slightly fewer, at 80.5 percent against 85.7. Published cut-offs range from 16 to 33 percent, which is worth knowing before you compare your result against a figure read somewhere else.
Where the cut-off sits changes the test
The classic rule pairs two things, which are a glycosylated share of 20 percent or less and a ferritin above the top of normal. That rule caught 70.5 percent of cases and cleared 83.2 percent. Raise the ferritin bar to five times normal and it becomes a different instrument, catching 43.2 percent and clearing 92.9 percent.
Count what that trade cost, because it is the point of the comparison. It spent 27 percentage points of catching to buy about ten points of clearing, which is not a good rate. For a disease you are hunting for rather than confirming, that is a bad exchange. The cases you lose are real people who have the disease and whose result now reads as normal to whoever is looking at it.
A high bar suits confirming a suspicion you already hold. It does not suit deciding whether to hold one in the first place. Knowing which of those two a test is being used for is what makes a cut-off useful, and a number quoted without its purpose attached is hard to read.
The complication ferritin is watched for
Macrophage activation syndrome is the most serious complication of this disease, and ferritin is the test used to watch for it. A cut-off of 3,500 micrograms per liter caught 85 percent of the people who had it. When it read below that cut-off, it was right 97 percent of the time.
That last figure is where the practical value sits, because a result under the cut-off makes the complication unlikely. That is what a watching test should do. Very high values at the start of the illness count too, and a ferritin above 10,448 micrograms per liter at diagnosis marked a raised risk of getting the complication later.
Those cut-offs are about the complication rather than about the diagnosis, and this page keeps them apart on purpose. A ferritin figure quoted as a diagnostic cut-off for Still's disease is the kind of claim that gets repeated until it sounds settled. Nothing on this page offers a diagnostic cut-off.
Exercise, diet, and two blanks somebody checked
No exercise study of any kind exists in adult-onset Still's disease. Somebody also searched the full text of the 2024 European guideline for four words, which were exercise, physical activity, rehabilitation, and physiotherapy. Not one of the four appears in it. The guideline covers the diagnosis, two kinds of drug that block interleukin-1 and interleukin-6, short steroid courses, and watching for complications.
The nearest evidence is a Cochrane review of exercise in juvenile idiopathic arthritis. That group takes in the childhood form related to this disease along with several other illnesses, in children rather than adults. It found no real benefit on how well people moved, on quality of life, on fitness, or on pain, and no short-term harm either.
No trial of any diet exists here either. What does reach you comes through your treatment, and anyone on a long steroid course falls under the 2017 American College of Rheumatology guideline. It strongly advises getting your calcium and vitamin D right, doing weight-bearing and strength-building exercise, stopping smoking, and drinking less.
Why function stays poor when the disease is quiet
A 2022 study compared quality of life in adult-onset Still's disease against healthy controls. The patients scored worse, even when their illness showed little or no sign of being active at the time. The physical parts of the SF-36, a general patient-reported quality-of-life questionnaire, dropped most clearly of all, and disability, tiredness, general health, pain, and overall state of health were all worse than in the controls.
It made little difference whether somebody had one episode or a long-running course of the illness. So this is not only about people whose disease has been hard to control. It is also not explained by inflammation that went uncontrolled, because it held when disease activity was low or absent.
That is the argument for working on your physical function on purpose, in an illness where the research can't tell you how. Feeling limited when your bloods look fine is written down in the research rather than unusual. So say it to whoever manages your care, because absorbing it on your own helps nothing.
Common misconceptions.
Myth. A very high ferritin confirms the diagnosis.
Reality. It does not, and the numbers say why. Ferritin cleared 85.7 percent of the people who did not have the disease, so about one in seven of them still test positive. Ferritin also rises in infection, in cancer, in liver disease, and when the body holds too much iron. The diagnosis rests on the fever, the rash, the joints, and ruling everything else out, so the blood test backs it up rather than settling it.
Myth. A normal ferritin rules it out.
Reality. It does not, because ferritin caught only 60.4 percent of cases. So roughly two in five people with the disease have a ferritin that never flags. Glycosylated ferritin does better at 74 percent, and it still misses about a quarter of the people who have it. A diagnosis missed because the ferritin looked fine is a real way for this illness to go badly wrong for somebody.
Myth. If my disease is controlled, I should feel well.
Reality. You may not, and the research says so rather than only patients. Patients scored worse on quality of life than healthy controls, even when their illness looked quiet, with the physical parts dropping most. Disability, tiredness, pain, and general health were all worse too. It made little difference whether somebody had one episode or a long-running course, so feeling limited when the numbers look fine is written down rather than unusual.
Myth. There's exercise guidance for this disease somewhere.
Reality. There is not, and somebody checked rather than assuming. The full text of the 2024 European guideline was searched for four words, which were exercise, physical activity, rehabilitation, and physiotherapy. Not one of the four is in it, and no exercise study of any kind exists in adult-onset Still's disease, of any design at all. So that is a blank somebody checked for rather than something this site failed to find.
Questions patients ask.
What does my ferritin result mean?
Less on its own than its reputation suggests. Ferritin caught 60.4 percent of cases and cleared 85.7 percent of the people who did not have the disease. Two other measures of how well it does came out at 0.778 and 11.32, which together describe a useful test rather than a decisive one. Ferritin also rises in infection, in cancer, in liver disease, and when the body holds too much iron.
What is glycosylated ferritin?
Some of the ferritin in your blood has sugar groups attached, and this test measures what share of it does. So the result is a percentage rather than an amount. In this disease that share falls, and a low percentage beside a high total tells you more than either alone. Glycosylated ferritin caught 74 percent of cases and cleared 80.5 percent, so it catches more and clears slightly fewer, and published cut-offs range from 16 to 33 percent.
Should the ferritin threshold be set higher?
It depends what you want it for, and for finding the disease the trade is a bad one. Pairing a low glycosylated share with a ferritin above the top of normal caught 70.5 percent of cases and cleared 83.2 percent. Asking for five times normal instead caught 43.2 percent and cleared 92.9 percent. So the change spent 27 points of catching to buy about 10 points of clearing.
What is macrophage activation syndrome?
A bad complication, in which the immune response ends of control. It is also why your ferritin keeps getting rechecked. A cut-off of 3,500 micrograms per liter caught 85 percent of the people who had it, and when it read below that cut-off it was right 97 percent of the time. One more figure is worth knowing, which is that a ferritin above 10,448 micrograms per liter at diagnosis marked a raised risk of getting the complication later.
Can exercise help?
The answer isn't known, and that is a finding somebody checked. No exercise study of any kind exists in adult-onset Still's disease, whether a randomized trial, a controlled trial, or a run of case reports. Somebody also searched the 2024 European guideline for four words, which were exercise, physical activity, rehabilitation, and physiotherapy, and not one of the four is anywhere in it. The nearest evidence is a Cochrane review in juvenile idiopathic arthritis, which found no benefit and no short-term harm.
Why do I feel so limited when my bloods are fine?
Because that is what the study of quality of life found in this illness, rather than something odd about you. Patients scored worse than healthy controls, even when their illness looked quiet, and the physical parts of the SF-36, a general patient-reported quality-of-life questionnaire, dropped most. Disability was worse, and so were tiredness, pain, and general health. It made little difference whether somebody had one episode or a long-running course of the illness.
Is there a diet for Still's disease?
No trial of any diet exists here at all. Anyone on a long steroid course falls under the 2017 American College of Rheumatology guideline, whatever put them there. It strongly advises getting your calcium and vitamin D right, and it advises weight-bearing and strength-building exercise too. So what does reach you comes through the drug rather than the diagnosis, and anything sold as a Still's disease diet is up against nothing at all.
What does the 2024 guideline cover?
Four things, and neither exercise nor diet is among them. It covers the diagnosis, two kinds of drug, one blocking interleukin-1 and the other blocking interleukin-6, then short steroid courses and watching for complications. So it is a treatment guideline in a rare disease, where getting the drugs right has been the priority. That is not a ruling that exercise and diet do not count, and it does mean there is no advice on either to point you at.
What should I take to my next appointment?
Three things, which are a fever, a new or changed rash, and any sense of being suddenly unwell in a new way. A flare of this disease hits your whole body rather than one sore joint, which is the distinction that counts. New joint pain that will not go away counts too. Long-running arthritis is one road this disease takes, and that needs treatment rather than something to work around.
References.
- Lee Y; Gyu Song G. Diagnostic accuracy of ferritin and glycosylated ferritin in adult-onset Still’s disease: a meta-analysis. Zeitschrift für Rheumatologie. 2025;84:234-240. 10.1007/s00393-025-01672-6Diagnostic accuracy meta-analysis of 8 studies
- Fautrel B; Le Moël G; Saint-Marcoux B et al. Diagnostic value of ferritin and glycosylated ferritin in adult onset Still's disease. The Journal of rheumatology. 2001;28:322-9. PMID 11246670Diagnostic accuracy study in adult-onset Still's disease versus a control group of patients with other conditions
- Javaux C; El-Jammal T; Neau P et al. Detection and Prediction of Macrophage Activation Syndrome in Still’s Disease. Journal of Clinical Medicine. 2021;11:206. 10.3390/jcm11010206Retrospective multicentre observational cohort of 206 patients with Still's disease
- Tada Y; Inokuchi S; Maruyama A et al. Are the 2016 EULAR/ACR/PRINTO classification criteria for macrophage activation syndrome applicable to patients with adult-onset Still’s disease?. Rheumatology International. 2018;39:97-104. 10.1007/s00296-018-4114-1Retrospective diagnostic accuracy study applying the 2016 sJIA MAS criteria to 76 adult-onset Still's disease patients
- Fautrel B; Mitrovic S; De Matteis A et al. EULAR/PReS recommendations for the diagnosis and management of Still's disease, comprising systemic juvenile idiopathic arthritis and adult-onset Still's disease. Annals of the Rheumatic Diseases. 2024;83:1614-1627. 10.1136/ard-2024-225851International guideline
- Takken T; Van Brussel M; Engelbert R et al. Exercise therapy in juvenile idiopathic arthritis. Cochrane Database of Systematic Reviews. 2008;2010. 10.1002/14651858.CD005954.pub2Cochrane systematic review and meta-analysis of randomised controlled trials
- Ruscitti P; Rozza G; Di Muzio C et al. Assessment of health-related quality of life in patients with adult onset Still disease: Results from a multicentre cross-sectional study. Medicine. 2022;101:e29540. 10.1097/MD.0000000000029540Multicentre cross-sectional case-control study
- Buckley L; Guyatt G; Fink H et al. 2017 American College of Rheumatology Guideline for the Prevention and Treatment of Glucocorticoid‐Induced Osteoporosis. Arthritis & Rheumatology. 2017;69:1521-1537. 10.1002/art.40137GRADE-based clinical practice guideline
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.