Editing Rheumatoid factor (section)

==Testing==
RF is tested by collecting blood in a plain tube (5&nbsp;mL is often enough). The serum is tested for the presence of RF. There are different methods available, which include [[nephelometry]], [[turbidimetry]], agglutination of gamma globulin-coated latex particles or [[erythrocyte]]s. RF is often evaluated in patients suspected of having any form of [[arthritis]], even though positive results can be due to other causes and negative results do not rule out disease. In combination with signs and [[symptom]]s, it can play a role in both diagnosis and disease [[prognosis]]. It is part of the usual disease criteria of [[rheumatoid arthritis]].<ref>{{EMedicine|article|331715|Rheumatoid Arthritis|workup}}</ref>

The presence of rheumatoid factor in serum can also indicate the occurrence of suspected autoimmune activity unrelated to rheumatoid arthritis, such as that associated with tissue or organ rejection. In such instances, RF may serve as one of several [[serology|serological]] markers for autoimmunity.<ref>{{cite journal |doi=10.1159/000013304 |title=Serological Markers of Autoimmunity in Renal Transplant Patients with Chronic Hepatitis C |year=1998 |last1=Rostaing |first1=Lionel |last2=Modesto |first2=Anne |last3=Cisterne |first3=Jean Marc |last4=Izopet |first4=Jacques |last5=Oksman |first5=Françoise |last6=Duffaut |first6=Michel |last7=Abbal |first7=Michel |last8=Durand |first8=Dominique |journal=American Journal of Nephrology |volume=18 |pages=50–6 |pmid=9481439 |issue=1|s2cid=6941129 }}</ref> The sensitivity of RF for established rheumatoid arthritis is only 60 to 70 percent with a specificity of 78 percent.<ref>{{cite journal|last1=Nishimura|first1=K|last2=Sugiyama|first2=D|last3=Kogata|first3=Y|last4=Tsuji|first4=G|last5=Nakazawa|first5=T|last6=Kawano|first6=S|last7=Saigo|first7=K|last8=Morinobu|first8=A|last9=Koshiba|first9=M|last10=Kuntz|first10=KM|last11=Kamae|first11=I|last12=Kumagai|first12=S|title=Meta-analysis: diagnostic accuracy of anti-cyclic citrullinated peptide antibody and rheumatoid factor for rheumatoid arthritis.|journal=Annals of Internal Medicine|date=5 June 2007|volume=146|issue=11|pages=797–808|pmid=17548411|doi=10.7326/0003-4819-146-11-200706050-00008|s2cid=6640507}}</ref>

Rheumatoid factor is part of the 2010 ACR/EULAR classification criteria for rheumatoid arthritis. RF positivity combines well with [[anti-CCP]] and/or 14-3-3η ([[YWHAH]]) to inform diagnosis.<ref> Zhang Y, Liang Y, Feng L, Cui L. Diagnostic performance of 14-3-3η and anti-carbamylated protein antibodies in Rheumatoid Arthritis in Han population of Northern China. Clin Chim Acta. 2020 Mar;502:102-110. doi: 10.1016/j.cca.2019.12.011. Epub 2019 Dec 17. PMID: 31862264. </ref> RF positivity at baseline has also been described as a good prognostic marker for future radiographic damage.<ref> Bukhari M, Lunt M, Harrison BJ, Scott DG, Symmons DP, Silman AJ. Rheumatoid factor is the major predictor of increasing severity of radiographic erosions in rheumatoid arthritis: results from the Norfolk Arthritis Register Study, a large inception cohort. Arthritis Rheum. 2002 Apr;46(4):906-12. doi: 10.1002/art.10167. PMID: 11953966. </ref>