Rheumatoid Arthritis (RA) Factor

CPT: 86431
Updated on 10/25/2017
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Test Details

Synonyms

  • RA Latex, Turbidimetry
  • RF Titer
  • Rheumatoid Factor (RF)

Use

Help in the differential diagnosis and prognosis of arthritic disorders

Limitations

Markedly lipemic or contaminated specimens may yield false-positive results.

Methodology

Latex immunoturbidimetry

Reference Interval

Negative: <14.0 IU/mL

Additional Information

Rheumatoid factors are antibodies directed against the Fc fragment of IgG. These are usually IgM antibodies, but may be IgG or IgA. Rheumatoid factor is present in the serum of a majority of patients with rheumatoid arthritis, depending in part on what method is used. Latex beads coated with human IgG will be positive in 70% to 85% (and have significant numbers of false-positives). Sheep RBCs coated with rabbit IgG will be positive in 60% to 70% (and have fewer false-positives). Many rheumatic conditions and other chronic inflammatory processes also may produce rheumatoid factors. The presence of rheumatoid factor, especially in low titer, is far from diagnostic for rheumatoid arthritis. Furthermore, with increasing age, people with no clinical illness may have rheumatoid factor. The presence of IgM RFs has been reported in as much as 10% of the normal population. Statistically, patients with rheumatoid arthritis who have high titer rheumatoid factor are more likely to have severe disease and systemic involvement than other patients. Rheumatoid factor can be detected in synovial fluid, pleural fluid, and pericardial fluid, but contributes little more than a positive serum test. Some rheumatoid factors may behave as cryoglobulins.

Specimen Requirements

Specimen

Serum or plasma

Volume

1 mL

Minimum Volume

0.5 mL

Container

Red-top tube, gel-barrier tube, lavender-top (EDTA) tube, or green-top (heparin) tube

Storage Instructions

Maintain specimen at room temperature.

Stability Requirements

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3

Causes for Rejection

Hemolysis; lipemia

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
006502 Rheumatoid Arthritis Factor 11572-5 006171 RA Latex Turbid. IU/mL 11572-5

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