Rheumatoid Factor Guidelines

Understanding Rheumatoid Factor Values

The American College of Rheumatology (ACR) and European League Against Rheumatism (EULAR) categorize RF results as negative (values less than or equal to the upper limit of normal), low positive (values higher than ULN but ≤3 times ULN), and high positive (values more than 3 times ULN), with the normal range for rheumatoid factor (RF) being less than or equal to the upper limit of normal (ULN) for the laboratory and assay, which is typically considered to be ≤14-15 IU/mL 1

The American College of Rheumatology (ACR) and European League Against Rheumatism (EULAR) include RF testing as part of the 2010 classification criteria for RA, contributing up to 3 points in the scoring system 2
RF should be interpreted alongside anti-citrullinated protein antibody (ACPA) status, as both are important serological markers for RA diagnosis and prognosis, and positive RF and/or ACPA are useful predictors of severe disease and poor prognosis in patients with RA 3, 4

Otras infecciones como mononucleosis infecciosa, citomegalovirus y parvovirus pueden causar resultados falsos positivos de FR 5
El Síndrome de Sjögren, lupus eritematoso sistémico y esclerosis sistémica pueden presentar FR positivo 6
Vasculitis de diferentes tamaños vasculares pueden mostrar positividad para FR 7
En pacientes tratados con inhibidores de puntos de control inmunitario (ICI), el FR suele estar ausente a pesar de manifestaciones reumáticas 7
En pacientes con artritis inducida por ICI, solo algunos son positivos para FR (rango 18-246 UI/mL) 7

RF positivity in rheumatoid arthritis correlates with disease severity, including higher frequency of rheumatoid nodules, progressive joint destruction, and worse prognosis, as stated by the European Heart Journal 8, 9

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