RFtiters

RF titers refer to the measured concentration of rheumatoid factor in the blood. Rheumatoid factor is an autoantibody that targets the Fc region of other IgG antibodies, most commonly of the IgM isotype, though IgG and IgA RF can occur. RF titers are typically reported as a dilution (for example, 1:40, 1:160) or in units per milliliter depending on the assay used. The titer is obtained using methods such as nephelometry, turbidimetry, ELISA, or latex agglutination.

Clinical interpretation of RF titers is nuanced. A positive RF test supports evaluation for rheumatoid arthritis but is not specific for the disease; detectable RF can be found in a substantial minority of healthy adults, particularly the elderly, and in several other conditions such as Sjögren syndrome, systemic lupus erythematosus, chronic infections, and chronic liver disease. Conversely, a person with rheumatoid arthritis may have a negative RF result, especially in early disease, leading to a seronegative classification. Therefore, RF results are interpreted in the context of clinical presentation and other laboratory tests.

In RA, RF is present in about 70–80% of patients overall, but anti-CCP (anti–citrullinated protein antibodies) tests provide greater specificity. RF titers do not reliably reflect disease activity or prognosis on their own; they may change with therapy in some individuals but are not a definitive activity marker. Laboratories may have varying reference ranges, so results should be interpreted with awareness of the specific assay’s thresholds.