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RHEUMATOID FACTOR (RA TEST)
(NPLEX)
The test is negative in one-third if patients with definite rheumatoid arthritis. It gives useful
objective evidence of rheumatoid arthritis, but a negative RA test does not rule out rheumatoid
arthritis.
It is positive in 5% of rheumatoid variants (arthritis associated with psoriasis, ulcerative colitis,
regional enteritis, Reiter's syndrome, juvenile rheumatoid arthritis, rheumatoid spondylitis).
It is positive in < 5% of normal persons; progressive increase with age < 25% of persons over age
70.
It may be positive in up to one-third of patients with SLE.
It may be positive in syphilis, chronic infections, viral infections, scleroderma, sarcoidosis, chronic
liver disease, subacute bacterial endocarditis, chronic pulmonary interstitial fibrosis, etc.
Use slide test only for screening; confirm positive test with tube dilution. Significant titer is > 1:80.
In rheumatoid arthritis, titers are often 1:640 to 1:5120 and sometimes < 1:320,000. Titers in
conditions other than rheumatoid arthritis are usually < 1:80.
RHEUMATOID ARTHRITIS
Serologic tests for rheumatoid factor (e.g., using latex, bentonite, or sheep or human RBCs).
Tests become positive after disease active for 6 months. Positive in 75% of "typical" cases;
positive in 95% of patients with subcutaneous nodules; high titers in patients with splenomegaly,
vasculitis, or neuropathy. Positive in only 10-20% of patients with juvenile rheumatoid arthritis.
May diminish or disappear during remission. Positive in 5% of normal population. False positive in
other diseases (e.g., SLE, sarcoidosis, liver diseases, subacute bacterial endocarditis, syphilis,
leprosy, tuberculosis). Negative in osteoarthritis, gout, ankylosing spondylitis, rheumatic fever,
suppurative arthritis, arthritis associated with ulcerative colitis.
Anemia is moderate in degree, of the normocytic hypochromic type, and not responsive to
administration of iron, folic acid, or vitamin B12 or to splenectomy.
Serum iron is decreased.
WBC is usually normal; there may be a slight increase early in the active disease.
Increased ESR and positive C-reactive protein (CRP) test are rough guides to activity and to
therapy.
Serum protein electrophoresis shows increase in globulins, especially in gamma and alpha2
globulins, and decreased albumin.
Positive LE test in < 20% of patients is usually weakly reactive. Antinuclear factors are present in
< 65% of patients, depending on sensitive of test.
Serum calcium, phosphorus, alkaline phosphatase, uric acid, and ASOT are normal.
Synovial biopsy is especially useful in monarticular form to rule out tuberculosis, gout, etc.
RA tests
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Comparison of Rheumatoid Arthritis and Osteoarthritis
Rheumatoid Arthritis
Osteoarthritis
Synovial fluid has high WBC
and low viscosity
Effusions infrequent
ESR more markedly increased
ESR may be mildly to moderately increased
Rheumatoid factor usually
present
RF usually absent
Positive biopsy of subcutaneous
rheumatoid nodule and synovia
Rheumatoid changes in tissue absent
RA tests