Diagnosis

Rheumatoid arthritis can be difficult to diagnose. Many other conditions resemble it and its symptoms can develop insidiously. Blood tests and x-rays may show normal results for months after the onset of joint pain. Even after rheumatoid arthritis has been diagnosed, it is extremely important to determine whether the course of the disease is benign (type 1) or aggressive (type 2) in order to treat the problem appropriately.

Blood Tests

Various blood tests may be used to help diagnose RA, determine its severity, and detect complications of the disease.

Rheumatoid Factor. In RA, antibodies that collect in the synovium of the joint are known as rheumatoid factor. In about 80% of cases of RA, blood tests reveal rheumatoid factor. It can also show up in blood tests of people with other diseases. However, when it appears in patients with arthritic pain on both sides of the body, it is a strong indicator of type 2 RA. The presence of rheumatoid factor plus evidence of bone damage on x-rays also suggests a significant chance for progressive joint damage.

Erythrocyte Sedimentation Rate Test. An erythrocyte sedimentation rate (ESR or sed rate) measures how fast red blood cells (erythrocytes) fall to the bottom of a fine glass tube that is filled with the patient's blood. The higher the sed rate the greater the inflammation. In addition to rheumatoid arthritis, the sed rate can be high in many conditions ranging from infection to inflammation to tumors. The test is used, then, not for diagnosis, but to help determine how serious the condition is.

C-Reactive Protein. High levels of C-reactive protein (CRP) are also indicators of active inflammation. However, because obesity also increases CRP levels, the doctor should consider a patient’s body mass index when evaluating CRP levels during RA diagnosis.

Anti-CCP Antibody Test. The presence of antibodies to cyclic citrullinated peptides (CCP) can identify RA years before symptoms develop. In combination with the test for rheumatoid factor, the CCP antibody test is the best predictor of which patients will go on to develop severe RA. Used in Europe, the test is now beginning to be used somewhat more commonly in the U.S. U.S. laboratories have not yet developed consistent standards for interpreting the test, however.

Tests for Anemia. Anemia is a common complication and blood tests should be taken that determine the amount of red blood cells (hemoglobin and hematocrit) and iron (soluble transferrin receptor and serum ferritin) in the blood.

Possible RA Markers in Synovial Fluid

Analyzing the synovial fluid might prove to be helpful in detecting markers of joint destruction, but this is not commonly performed. Some investigational examples include the following:

• An enzyme called MMP-3 (matrix metalloproteinase 3) is involved with the degradation of cartilage. Its presence in synovial fluid is strongly associated with progressive joint destruction in patients with chronic RA.
• High levels urocortin, a member of the peptide family involved in the stress response, may also be a major player in the RA inflammation.

Imaging Techniques

X-Rays. X-rays generally have not been helpful to detect the presence of early rheumatoid arthritis because they cannot show images of soft tissue. The use of a technique known as dual energy x-ray absorptiometry, however, may be useful in detecting early bone loss in rheumatoid arthritis (2 - 27 months after onset). Evidence of damage on x-rays along with elevated rheumatoid factor is a significant predictor for progressive joint destruction.

Ultrasound. Special ultrasound techniques called power Doppler ultrasonography (PDUS) or quantitative ultrasound (QUS) may be helpful in RA. PDUS may be reliable for monitoring inflammatory activity in the joint. QUS, which is used for osteoporosis, has been used to detect bone loss in fingers, which may prove to be a good indicator of early RA.

Magnetic Resonance Imaging. Specially designed magnetic resonance imaging (MRI) equipment called extremity MRI may be able detect bone erosions in the hands of RA patients where x-rays cannot. Further evaluation is necessary.

Ruling Out Other Disorders

Symptoms of rheumatoid arthritis can be mimicked by things as benign as a bad mattress or as serious as cancer. A number of rare genetic diseases attack the joints. Physical injuries, infections, and poor circulation are among the many problems that can cause aches and pains. It would be impossible to discuss in this report the dozens of other conditions that present themselves with symptoms of joint aches and pains.

Osteoarthritis. Osteoarthritis requires some special mention because it is the most common form of arthritis. It differs from RA in several important respects.

• Osteoarthritis usually occurs in older people.
• It is located in only one or a few joints. (In fact, osteoarthritis is probably most often confused with rheumatoid arthritis if it affects multiple joints in the body.)
• The joints are less inflamed.
• Progression of pain is almost always gradual.

Gout. Gout also causes swelling and severe pain in a joint, although most commonly starting in one joint. It is particularly difficult to distinguish chronic gout in older people from rheumatoid arthritis, however, since gout in this population can occur in a number of joints. A proper diagnosis can be made with a detailed medical history, laboratory tests, and detection in the affected joint of a salt called monosodium urate (MSU), which identifies gout.

Diseases with Symptoms Similar to Rheumatoid Arthritis
Disease	Specific Subtypes
Osteoarthritis
Infectious Arthritis	Lyme disease, septic arthritis, bacterial endocarditis, mycobacterial and fungal arthritis, viral arthritis
Postinfectious or Reactive Arthritis	Reiter syndrome (a disorder characterized by arthritis and inflammation in the eye and urinary tract), rheumatic fever, inflammatory bowel disease
Crystal Induced Arthritis	Gout and pseudogout
Other rheumatic Autoimmune Diseases	Systemic vasculitis, systemic lupus erythematosus, scleroderma, Still's Disease (also called juvenile rheumatoid arthritis) Behcet's disease
Fibromyalgia
Other Diseases	Chronic fatigue syndrome, hepatitis C, familial Mediterranean fever, cancers, AIDS, leukemia, bunions, Whipple's disease, dermatomyositis, Henoch-Schonlein purpura, Kawasaki's disease, erythema nodosum, erythema multiforme, pyoderma gangrenosum, pustular psoriasis