How Rheumatoid Arthritis Is Diagnosed: Criteria and Tests

Rheumatoid arthritis is diagnosed by combining a clinical examination for swollen joints with rheumatoid factor and anti-CCP (anti-cyclic citrullinated peptide) antibody levels, symptom duration and inflammatory markers, scored under the 2010 ACR/EULAR classification criteria. A score of 6 or more out of 10 classifies definite rheumatoid arthritis. Dr. Sajal Ajmani, HOD – Rheumatology, Manipal Hospital, Dwarka, New Delhi, India, stressed that serology supports the diagnosis but does not make it on its own.

This article covers the diagnostic half of Dr. Ajmani's masterclass: why the old criteria were replaced, how the 2010 system is scored, where ultrasound helps, why antibody results mislead, and how to recognise palindromic rheumatism and preclinical disease. For the overall picture, including how disease activity is measured once the diagnosis is made, see the complete guide to rheumatoid arthritis.

The 1987 ACR criteria and why they fell short

Most doctors learned the 1987 criteria of the American College of Rheumatology (ACR) at medical school. They list seven items, of which four had to be present:

1. Morning stiffness in and around the joints, lasting at least an hour.
2. Arthritis of three or more joint areas.
3. Arthritis of the hand joints (wrist, metacarpophalangeal or proximal interphalangeal joints).
4. Symmetric arthritis, affecting the same joint areas on both sides.
5. Rheumatoid nodules, firm lumps under the skin over bony prominences.
6. A positive rheumatoid factor.
7. Radiographic changes typical of rheumatoid arthritis on hand and wrist X-rays.

The first four items had to be present for at least six weeks.

Dr. Ajmani identified the core weakness: several items appear only late in the disease. Radiographic changes are usually a late sign. Rheumatoid nodules also come late. Even arthritis in three joint areas, or symmetry, may be absent in the first weeks. The criteria also predate the anti-CCP antibody, which did not exist in 1987 and so had no place in them.

The consequence is measurable. In early rheumatoid arthritis, Dr. Ajmani put the sensitivity of the 1987 criteria at only 50%: half of patients with genuine early disease would not be classified. A system that confirms the disease only once joints are already damaged defeats the purpose of early treatment.

The 2010 ACR/EULAR criteria for rheumatoid arthritis

To pick up rheumatoid arthritis earlier, the ACR and the European Alliance of Associations for Rheumatology (EULAR, formerly the European League Against Rheumatism) published new criteria in 2010.

Who the criteria apply to

Two conditions must be met before the criteria are applied. First, the patient must have at least one swollen joint, meaning clinical synovitis (inflammation of the joint lining). Second, the swelling must not be better explained by another disease, such as gout, psoriatic arthritis or lupus.

The four scoring domains

Dr. Ajmani described four things to assess in the patient.

Joint involvement. Both the number and the type of joints count. Large joints are the shoulders, elbows, hips, knees and ankles; small joints are those of the hands and wrists and the small joints of the feet.

• One large joint (for example, only the knee is swollen): 0 points
• Two to ten large joints: 1 point
• One to three small joints: 2 points
• Four to ten small joints: 3 points
• More than ten joints, including at least one small joint: 5 points

Serology. Rheumatoid factor and anti-CCP antibody levels are scored together.

• Both negative: 0 points
• Low positive, meaning above the upper limit of normal but no more than three times it: 2 points
• High positive, meaning more than three times the upper limit of normal: 3 points

Symptom duration.

• Less than six weeks: 0 points
• Six weeks or more: 1 point

Acute phase reactants. These are the ESR (erythrocyte sedimentation rate) and CRP (C-reactive protein), the routine blood markers of inflammation.

• Both normal: 0 points
• Either raised: 1 point

Reading the score

A score of 6 or more out of 10 classifies the patient as having definite rheumatoid arthritis. A patient who scores below 6 is not excluded. Dr. Ajmani made two points here: the patient may fulfil the criteria later as the disease evolves, and a careful history may reveal that other joints were swollen in the past, which can bring the patient over the threshold.

Each domain takes the highest category the patient reaches; points are not added within a domain. A patient with four swollen small joints, a high-positive anti-CCP, eight weeks of symptoms and a raised CRP scores 3 + 3 + 1 + 1 = 8, which classifies as definite disease.

What the new criteria gained and what they cost

According to Dr. Ajmani, the 2010 criteria have a good sensitivity of 80%, against the 50% of the 1987 criteria in early disease, but a lower specificity of 70%. The trade-off is deliberate. Capturing more early cases means that some patients with other inflammatory arthritides will also score 6 or more. The criteria were designed to classify patients for research, and when they are used to support a diagnosis in an individual patient, the clinician's judgement about alternative causes remains decisive. This is why the second entry condition, that no other disease better explains the synovitis, carries as much weight as the score itself.

Ultrasound with Doppler in diagnosing rheumatoid arthritis

Newer imaging can detect synovitis that the examining hand misses. Dr. Ajmani highlighted musculoskeletal ultrasound, which can show erosions, can detect early synovial disease, and complements the plain X-ray in diagnosing rheumatoid arthritis.

He illustrated the point with an ultrasound of a wrist that showed synovial thickening; when Doppler was applied, the thickened synovium showed increased blood flow, the signature of active inflammation. Doppler signal of this kind distinguishes active synovitis from old, burnt-out thickening, and it can confirm that a doubtful joint is genuinely swollen, which matters when a single joint decides whether a patient crosses the entry threshold of the criteria. Ultrasound detects bone erosions earlier than plain radiographs.

Rheumatoid factor and anti-CCP: why a positive test is not a diagnosis

"Rheumatoid arthritis is a clinical diagnosis" was the sentence Dr. Ajmani most wanted his audience to retain. Just because rheumatoid factor is positive does not mean the patient has rheumatoid arthritis; the result must be clinically correlated.

What causes a positive rheumatoid factor without rheumatoid arthritis

Rheumatoid factor is an antibody directed against part of the body's own immunoglobulin G. Dr. Ajmani listed conditions in which it can be positive without rheumatoid arthritis:

• tuberculosis
• infective endocarditis
• hepatitis B and hepatitis C
• normal people above the age of 70

What causes a positive anti-CCP without rheumatoid arthritis

Anti-CCP antibodies are more specific for rheumatoid arthritis than rheumatoid factor, with a specificity of around 95% against roughly 85% for rheumatoid factor in pooled studies. They are still not infallible. Dr. Ajmani noted that anti-CCP can also be positive in:

• psoriatic arthritis
• hepatitis B and hepatitis C
• tuberculosis

The list has particular force for doctors practising where tuberculosis and viral hepatitis are common. A patient with joint pain, a positive rheumatoid factor and an undiagnosed chronic infection is at real risk of being started on immunosuppressive treatment that could make the infection worse. Serology should be ordered to answer a clinical question raised by swollen joints, not as a screening test for aches and pains.

Palindromic rheumatism

Palindromic rheumatism is a form of inflammatory arthritis in which brief, intense attacks of joint inflammation last from a few hours to a few days, usually in a single joint, and resolve completely.

Palindromic rheumatism vs gout

An attack can mimic gout, and Dr. Ajmani gave a practical distinction: in gout, pain and swelling usually last for more than two days, whereas in palindromic rheumatism they last less than two days. He noted that rheumatoid factor and anti-CCP are positive in palindromic rheumatism; in published series they are found in a substantial proportion of patients, though not in all, and their presence raises the risk of progression.

His working description for the clinic is specific. A patient who presents with repeated attacks of pain and swelling in a single joint, is free of symptoms between attacks, and has a normal uric acid with a raised rheumatoid factor has palindromic rheumatism.

Does palindromic rheumatism progress to rheumatoid arthritis?

According to Dr. Ajmani, one-third of patients with palindromic rheumatism progress to rheumatoid arthritis. The condition is therefore not a benign curiosity but, for many patients, an early form of rheumatoid disease that deserves follow-up.

Palindromic rheumatism treatment

Asked during the session what to use for palindromic rheumatism, Dr. Ajmani answered that he uses hydroxychloroquine. Hydroxychloroquine is a well-tolerated conventional DMARD, but long-term use carries a small risk of retinal toxicity. Ophthalmology guidance recommends a baseline eye examination and annual screening after five years of use, and a daily dose of no more than 5 mg per kg of actual body weight.

Preclinical rheumatoid arthritis

Preclinical rheumatoid arthritis, as Dr. Ajmani defined it, is a period of autoimmunity before joint symptoms develop, during which there is subclinical inflammation. The patient may have joint pains, but none of the joints is swollen. In these patients, a positive anti-CCP signals a high chance of progression to rheumatoid arthritis.

The autoantibodies of rheumatoid arthritis can appear in the blood years before the first swollen joint. A patient with joint pains and a positive anti-CCP but no synovitis does not meet the entry condition of the 2010 criteria and cannot be classified. The right response is close follow-up and a low threshold for re-examination, so that the first genuinely swollen joint is caught within the window of opportunity for early treatment.

How rheumatoid arthritis is diagnosed: the sequence in practice

Taken together, the points from the masterclass give a clear order for assessing a patient with suspected rheumatoid arthritis:

1. Examine the joints and establish whether at least one is genuinely swollen; use ultrasound with Doppler where examination is doubtful.
2. Consider and exclude the diseases that better explain the synovitis, including gout and infection.
3. Measure rheumatoid factor, anti-CCP, ESR and CRP, and interpret positive antibodies in the light of tuberculosis, hepatitis B and C, endocarditis and age.
4. Score the 2010 criteria, and if the patient falls short, re-evaluate over time and take a careful history of past joint swelling.
5. Recognise the atypical presentations: brief single-joint attacks suggest palindromic rheumatism, and joint pain with positive anti-CCP but no swelling suggests preclinical disease.

Once the diagnosis is made, treatment should start without delay; the treat-to-target DMARD strategy sets out how. The questions raised during the live session, including the one on palindromic rheumatism, are on the masterclass Live Discussion page.