- Gel barrier or red top tube
- 5-7 mL of venous blood
Additional information
- Handle sample gently to prevent hemolysis
- Reject lipemic sample
- The Rheumatoid Factor (RF) test detects the presence and levels of RF antibody in the blood
- RF is an anti–gamma-globulin autoantibody usually of IgM class and occasionally of IgG or IgA class. This antibody reacts (binds) to the Fc fragment of IgG to form immune complexes
- Assay techniques used to detect RF include:
- Agglutination of immunoglobulin coated particles (visual assay)
- Latex particle enhanced nephelometry
- The clinical utility of the rheumatoid factor (RF) test includes:
- To aid in the diagnosis and evaluation of rheumatoid arthritis (RA)
- To differentiate RA from other forms of arthritis
- For detection of RF in other connective tissue and autoimmune disorders
- Titers can be useful in assessing disease severity and response to therapy
- Initially, patients are screened for the presence of RF. If RF is detected, a titration is performed
- It remains unclear whether RF itself directly causes the destructive changes associated with RA, or is incidental to these changes and could even serve some beneficial purpose
- Absence of RF does not exclude the diagnosis RA as it is a sensitive but nonspecific test
- 5-8% of normal individuals are positive for RF and 15-20% of RA are seronegative for RF
- It is typically for RF to be absent when the first clinical signs and symptoms of RA occur
- Early seroconversion to positive RF is predictive of a greater risk of articular destruction and a sustained disabling course of disease
- RF incidence increases with duration of disease in rheumatoid arthritis
- 3 Months: 33%
- 6 months: 45%
- 1 year: 75%
- 18 months: 90%
- RF is used as a marker for persistence of polyarticular juvenile rheumatoid arthritis into adulthood
Additional information
- Higher values of RF are seen in older individuals (>65 yrs)
- Incidence of RF increases with age
- Conditions not associated with RF include:
- Ankylosing spondylitis
- Chondrocalcinosis
- Enteropathic arthritis
- Gout
- Osteoarthritis
- Psoriatic arthritis
- Suppurative arthritis
- Reiter's syndrome
- Related laboratory tests include:
- Antinuclear antibodies (ANA)
- C-reactive protein
- Cyclic citrullinated peptide antibody (CCP)
- Erythrocyte sedimentation rate (ESR)
- Synovial fluid analysis
- Uric acid
Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below.
Nephelometry Method
| Conv. Units (U/mL) | SI Units (kU/L) |
|---|---|
| <20 | <20 |
Agglutination Method
| Titers | |
|---|---|
| <16 years | <1:20 |
| 16-65 years | <1:40 |
| >65 years | <1:80 |
Conditions associated with elevated RA factor include:
- Rheumatoid arthritis (75-90%)
- Collagen-vascular diseases
- Felty's syndrome
- Cryoglobulinemia (40-100%)
- Dermatomyositis (10%)
- Polyarteritis nodosa
- Polymyositis (10%)
- Sarcoidosis
- Scleroderma (20-30%)
- Sjögren's syndrome (80-90%)
- Systemic lupus erythematosus (15-35%)
- Waldenström macroglobulinemia
- Infectious conditions
- Bacterial endocarditis (SBE)
- Influenza
- Infection following vaccination
- Kala-azar
- Leprosy
- Leishmaniasis
- Lymphoma
- Malaria
- Osteomyelitis
- Syphilis
- Tuberculosis
- Viral infections
- Adenovirus
- HIV
- HCV
- Mononucleosis
- Hepatic disorders
- Acute and chronic hepatitis
- Cirrhosis
- Primary biliary cirrhosis
- Other conditions
- Nephrotic syndrome
- Renal disease
- Adult Still's disease
- Diffuse interstitial pulmonary fibrosis
- Juvenile chronic arthritis
- Malignancy
- Myocardial infarction
- Skin and renal allograft patients
- Thyroid diseases
- Drugs
- Methyldopa
Causes of false positive values include:
- Inadequately activated complement
- Individuals who have received multiple vaccinations
- Recent transfusion or multiple transfusions
- Serum with high lipid or cryoglobulin levels
- False negative values can occur with high serum IgG levels
- Bobbio-pallavicini F et al. High IgA Rheumatoid factor levels are associated with poor clinical response to TNF-{alpha} inhibitors in rheumatoid arthritis. Ann Rheum Dis. 2006 Nov 1; [Epub ahead of print].
- Greiner A et al. Association of anti-cyclic citrullinated peptide antibodies, anti-citrullin antibodies, and IgM and IgA rheumatoid factors with serological parameters of disease activity in rheumatoid arthritis. Ann N Y Acad Sci. 2005;1050:295-303.
- Katwa G et al. False positive elevation of cardiac troponin I in seropositive rheumatoid arthritis. J Rheumatol. 2001;28:2750-1.
- Kobayashi Y et al. [Serum rheumatoid factor and peripheral blood eosinophil counts in patients with bronchial asthma] [Article in Japanese]. Arerugi. 2004;53:1210-5.
- LabTestsOnline®. Rheumatoid Factor. [Homepage on the Internet] ©2001-2006. Last reviewed on September 30, 2006. Last accessed on November 8, 2006. Available at URL: http://www.labtestsonline.org/understanding/analytes/rheumatoid/sample.html
- Spadaro A et al. Interleukin-13 in autoimmune rheumatic diseases: relationship with the autoantibody profile. Clin Exp Rheumatol. 2002;20:213-6.
- UTMB Laboratory Survival Guide®. RHEUMATOID FACTOR, serum. [Homepage on the Internet]© 2006. Last reviewed on February 2006. Last accessed on November 21, 2006. Available at URL: http://www.utmb.edu/lsg/LabSurvivalGuide/chem/RF.html