To determine the presence of 19S gamma globulins directed against IgG Immunoglobulins, to support the diagnosis of rheumatoid arthritis, to evaluate ankylosing spondylitis and sacroilitis. Strong positivity with low ANA usually means rheumatoid arthritis.
< 12 IU/mL
A very low value may exist in a variety of other diseases. Weak RF, high ANA and anti-n-DNA, and low complement levels may indicate SLE. Weak RF and low ANA may indicate cryoglobulinemia, vasculitis, or both. RF is not specific for a diagnosis of rheumatoid arthritis. There are numerous cases of sero-negative rheumatoid arthritis. Patients with collagen diseases other than RA may have RF.
- RF Test
- Rheumatoid Arthritis
- Rheumatoid Factor
- SCAT Replacement Assay
- Sheep Cell Agglutination Titer Replacement Assay
Collect blood in SST tube. Centrifuge, aliquot serum into a plastic vial and refrigerate. Fluids are not acceptable.
False negatives or weak reactions may be attributed to early or chronic stages of the disease or to therapy. False positives may occur in pulmonary TB, SLE, aging, syphilis, cirrhosis, infectious hepatitis, viral infections, mixed cryoglobulinemia, and myeloproliferative disorders. RF is reported in 70-80% of clinically diagnosed RA cases. Some rheumatoid factors react as cryoglobulins and may be a clue to the presence of cryoglobulinemia. These are anti-IgG antibodies complexed with IgG that form precipitates at low temperatures.