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Laboratory: Clinical Immunology
Test Name:
Test Code: RF
Clinical Information:
Alternate Name(s): RA (Rheumatoid Arthritis) Factor, RF (Rheumatoid Factor), Rheumatoid Arthritis

Measurement of rheumatoid factor may aid in the diagnosis of rheumatoid arthritis.
Rheumatoid factors are a heterogeneous group of high molecular weight auto-antibodies directed against the body’s own immunoglobulins. They are produced by plasma cells present at sites of tissue injury. The initiating antigen is thought to be one or more viruses or viral antigens that persist in the joint tissues. Research has shown that both environmental and genetic factors can affect the production of rheumatoid factors with various biological properties. Rheumatoid factors have also been observed in the serum of patients with lupus erythematosus, hepatitis, liver cirrhosis, syphilis and various other conditions but the RF titre is much lower than in rheumatoid arthritis (RA). Between 60 and 80% of patients with active RA possess this abnormal protein in their blood and joint fluid, and its detection is therefore of value in the diagnosis and monitoring of the disease.
Values should be used in conjunction with other laboratory and clinical findings.

Collection Devices:
Specimen Required:
Serum: 1.0 mL
Pediatric Serum: 0.5 mL

Refrigerated: 14 days
Frozen: 30 days
Serum: 1.0 mL
Pediatric Serum: 0.5 mL

Separate serum and ship refrigerated, or frozen if greater than 7 days from time of collection.

Testing Laboratory (MB): Health Sciences Centre Immunology Laboratory
Reference Values:
All Ages: 0.0 – 12.5 IU/ml
Reference value adopted from Binding Site, Optilite Rheumatoid Factor Kit, INS151.OPT, ver 21st March 2016

Method of Analysis: Turbidimetry – Binding Site Optilite
See Also:
More Information:
This assay is designed to detect IgM-RF.  Other immunoglobulin classes of RF will therefore not be detected.
Reportable Range: 7.0 – 6500.0 IU/ml
Undetected antigen excess is a rare event but cannot be excluded. If these free light chain results do not agree with other clinical or laboratory findings, or if the sample is from a patient that has previously demonstrated antigen excess, the result must be checked by retesting at a higher sample dilution. Results should always be interpreted in conjunction with other laboratory tests and clinical evidence; any anomalies should be discussed with the laboratory.