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UW Health SMPH
American Family Children's Hospital

UW Hospital and Clinics Lab Test Directory

Test Name: Rheumatoid Factor

Test Code(s): RA / RF

CPT Code(s): 86431

Methodology: Nephelometry

Request Form: UWHC Laboratory Request Form (UWH 1289220, 4004202); Write in test if not on form.

Days Performed: Daily, 24 hours.

Turnaround Time: Stat: 1 hour.
Routine: 4 hours.

Specimen Requirements

Specimen: Blood

Collection Container: Preferred: Red cap with yellow ring (SST)
Also Acceptable: Red top

Collection Volume: Preferred: 3 mL
Pediatrics: 1 mL

Volume Required: Preferred: 1 mL
Pediatrics: 0.3 mL

Specimen Processing: Centrifuge. Transfer cell-free serum to plastic vial.

Specimen Transport: Transport specimen to UWHC Core Laboratory (B4/220). Transport with coolant pack if coming from outreach location; avoid freezing.

Stability: Refrigerated: 7 days
Frozen: 3 months at or below -20C (freeze within 24 hours and avoid repeated freeze-thaw cycles)


Reference Interval:

Ages 0 days and up:  less than 15 IU/mL


Note:  Assay performance not established for pediatric population.

Additional Information:

A negative result does not exclude rheumatoid arthritis. Approximately 25% of patients with a diagnosed case of rheumatoid arthritis may present with a negative result for RF.


Certain non-rheumatoid conditions, connective tissue disorders and a variety of other disease states such as hepatitis may elicit a positive RF test.


Autoimmune antibodies common with other systemic autoimmune diseases were not assessed.


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