Rheumatoid Factor (RF)

Serum Rheumatoid Factor, Serum RF

Test Codes

EPIC: LAB12310394, Beaker: RFSER, Antrim: 30690

Department

Chemistry

Specimen Collection Criteria

Collect: One Gold-top SST tube.

Physician Office/Draw Specimen Preparation

Let specimen clot 30-60 minutes then immediately centrifuge to separate serum from cells. Refrigerate (2-8°C or 36-46°F) the centrifuged collection tube within two hours of collection.

Preparation for Courier Transport

Transport: Centrifuged collection tube, refrigerated (2-8°C or 36-46°F). (Minimum: 0.5 mL)

Rejection Criteria

• Grossly lipemic specimens.
• Hemolyzed specimens.
• Plasma specimens.

In-Lab Processing

Let specimen clot 30-60 minutes then immediately centrifuge to separate serum from cells. Deliver immediately to the appropriate testing station.

Storage

Specimen Stability for Testing:

Centrifuged SST Tubes and Microtainers^® with Separator Gel
Room Temperature (20-26°C or 68-78.8°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): Unacceptable

Red-top Tubes and Microtainers^® without Separator Gel
Room Temperature (20-26°C or 68-78.8°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable

Serum Specimens (Pour-Overs)
Room Temperature (20-26°C or 68-78.8°F): 2-4 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): 3 months

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days

Laboratory

Farmington Hills Chemistry Laboratory
Royal Oak Automated Chemistry Laboratory

Performed

Sunday – Saturday, 24 hours a day.
Results available within 24 hours.

Reference Range

Less than 15 IU/mL.

Test Methodology

Nephelometry.

Interpretation

• A negative RF test does not exclude rheumatoid arthritis (RA) nor does a positive test confirm it. RF may be found with many diverse chronic inflammatory diseases including a number of autoimmune diseases, and infections. RF is also found in a number of non-rheumatic conditions.
• RF is positive in 80-90% of RA patients within 18 months of diagnosis. Twenty percent of RA patients are RF-negative. These patients are said to have seronegative rheumatoid arthritis. Two to 3% of patients without RA have a false-positive RF test. Less than 25% of juvenile rheumatoid arthritis patients are RF-positive.
• High RF titers may indicate more aggressive disease.
• Treatment with some drugs especially penicillamine lowers RF titers. This decreased RF level may correlate with clinical improvement of the patient. About 50% of RA patients in remission have no detectable serum RF while 35% maintain high RF titers.

Clinical Utility

Rheumatoid factor assay is one of the most frequently requested tests in the clinical investigation of patients with joint symptoms. Rheumatoid factor (RF) is usually an IgM autoantibody that reacts with the Fc portion of IgG. In the presence of pathogen-specific IgG antibodies, IgM RF can produce false-positive results in IgM assays. RF is not a screening test. The test performs poorly when applied to the general population.

Clinical Disease

• Rheumatoid arthritis (RA) is a chronic, multisystem, autoimmune disease of unknown etiology. This disease is hallmarked by cartilage destruction, bone erosions, and joint deformities. Patients have a persistent inflammatory synovitis usually involving the joints in a symmetric pattern. The course of RA is variable.
• Rheumatoid arthritis is found worldwide and affects all races equally. The incidence increases with age and is five times greater in females than in males. Eighty percent of patients develop rheumatoid arthritis between the ages of 35 and 50 years of age. Severe RA is found at approximately four times the expected rate in first- degree relatives of individuals with seropositive disease. In the U.S. approximately 1% of the population (2.5 million people) have RA.

CPT Codes

86431

Contacts

Last Updated

3/31/2025