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Diagnostic Tests – Rheumatoid Factor (RF)
1. What disease is it associated with?
Rheumatoid factor (RF) is most commonly associated with rheumatoid arthritis (RA). It is present in over 70% of patients with RA, making it a useful supportive test. However, RF is not specific for RA and may also be positive in other autoimmune diseases, chronic infections, and even in some healthy older adults.
2. When do you answer rheumatoid factor?
You should select RF testing when the clinical scenario describes:
Symmetric small-joint inflammatory arthritis with morning stiffness → think rheumatoid arthritis → order rheumatoid factor (often along with anti-CCP antibodies).
1. What disease is it associated with?
Rheumatoid factor (RF) is most commonly associated with rheumatoid arthritis (RA). It is present in over 70% of patients with RA, making it a useful supportive test. However, RF is not specific for RA and may also be positive in other autoimmune diseases, chronic infections, and even in some healthy older adults.
2. When do you answer rheumatoid factor?
You should select RF testing when the clinical scenario describes:
- A woman with symmetric inflammatory arthritis
- Morning stiffness that improves with activity
- Involvement of the wrists, metacarpophalangeal (MCP) joints, and proximal interphalangeal (PIP) joints
- Laboratory evidence of inflammation, such as:
- Elevated ESR
- Synovial fluid WBC count between 2,000 and 20,000 cells/µL (inflammatory range)
Symmetric small-joint inflammatory arthritis with morning stiffness → think rheumatoid arthritis → order rheumatoid factor (often along with anti-CCP antibodies).
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