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Rheumatoid factor

The role of rheumatoid factor (RF) in the body

Rheumatoid factor (RF) is an autoantibody (usually IgM, rarely IgG or IgA) that mistakenly attacks its own immunoglobulins G (IgG). Its main functions are:

  1. Marker of autoimmune processes:
  • Binds to the Fc fragment of IgG, forming immune complexes that provoke inflammation.
  1. It is involved in the pathogenesis of rheumatoid arthritis (RA):
  • It damages joints, blood vessels, and other tissues.
  1. It may be present normally (in 2-5% of healthy people, especially the elderly).

Norm of rheumatoid factor in the blood

Assay MethodNormal Range (IU/ml)
ELISA/Nephelometry< 14–20
Latex Test< 1:40 (titer)

Interpretation:

  • Increased RF:
  • > 20 IU / ml – suspected autoimmune disease.
  • > 50 IU / ml – high probability of RA or other systemic diseases.
  • False positive results are possible for infections (hepatitis, tuberculosis).

Increased rheumatoid factor

Reasons:

  1. Autoimmune diseases:
  • Rheumatoid arthritis (60-80% of patients).
  • Sjogren ‘s syndrome(75-95%).
  • SLE (systemic lupus erythematosus, 15-30%).
  1. Infections:
  • Hepatitis B / C, endocarditis, tuberculosis.
  1. Other states:
  • Sarcoidosis, cirrhosis of the liver.

Symptoms (depending on the disease):

  • With RA:
  • Morning joint stiffness > 30 min.
  • Pain in small joints (hands, feet).
  • Late-stage joint deformities.
  • For Sjogren’s syndrome:
  • Dry eyes and mouth.
  • Joint pain.

Reduced rheumatoid factor

RF deficiency is not a pathology and does not cause symptoms.

  • In healthy people, RF may be absent.
  • Seronegative rheumatoid arthritis (20-30% of patients with RA do not have RF).

How do I normalize the level?

With increased RF:

  1. Treatment of the underlying disease:
  • RA: methotrexate, biologics (infliximab).
  • Sjogren‘s syndrome: immunosuppressants, artificial tears.
  1. Control of inflammation:
  • NSAIDs (ibuprofen – – for pain relief.
  • Glucocorticoids (prednisone) – for severe inflammation.

In the absence of RF, but with RA symptoms:

  • They check for anti-CCP (ACPA) , a more specific marker of RA.

When should I take the test?

  • For pain and swelling of the joints.
  • For dry eyes/mouth (suspected Sjogren).
  • For differential diagnosis of autoimmune diseases.

Important:

  • RF is not a 100% confirmation of RA – a complex of tests is needed (anti-CCP, CRP, X-ray of joints).
  • In children, RF is more often associated with infections, rather than with autoimmune processes.

Example:
RF 60 IU / ml + anti-CCP (+) + symmetric arthritis → diagnosis of rheumatoid arthritis.