Editing Rheumatoid arthritis (section)

===Blood tests===
When RA is clinically suspected, a physician may test for [[rheumatoid factor]] (RF) and [[anti-citrullinated protein antibodies]] (ACPAs measured as anti-CCP antibodies).<ref>{{cite journal | vauthors = Westwood OM, Nelson PN, Hay FC | title = Rheumatoid factors: what's new? | journal = Rheumatology | volume = 45 | issue = 4 | pages = 379–385 | date = April 2006 | pmid = 16418203 | doi = 10.1093/rheumatology/kei228 | doi-access = free }}{{subscription required}}</ref>{{rp|382}}
The test is positive approximately two-thirds of the time, but a negative RF or CCP antibody does not rule out RA; rather, the arthritis is called ''[[seronegative]]'', which occurs in approximately a third of people with RA.<ref>{{cite journal | vauthors = Salman E, Çetiner S, Boral B, Kibar F, Erken E, Ersözlü ED, Badak SÖ, Bilici Salman R, Sertdemir Y, Çetin Duran A, Yaman A | title = Importance of 14-3-3eta, anti-CarP, and anti-Sa in the diagnosis of seronegative rheumatoid arthritis | journal = Turkish Journal of Medical Sciences | volume = 49 | issue = 5 | pages = 1498–1502 | date = October 2019 | pmid = 31651120 | pmc = 7018368 | doi = 10.3906/sag-1812-137 }}</ref> During the first year of illness, rheumatoid factor is more likely to be negative with some individuals becoming seropositive over time. RF is a non-specific antibody and seen in about 10% of healthy people, in many other chronic infections like [[hepatitis C]], and chronic autoimmune diseases such as [[Sjögren's syndrome]] and [[systemic lupus erythematosus]]. Therefore, the test is not [[Specificity (tests)|specific]] for RA.<ref name="McGraw Hill"/>

Hence, new serological tests check for anti-citrullinated protein antibodies ACPAs. These tests are again positive in 61–75% of all RA cases, but with a specificity of around 95%.<ref>{{cite journal | vauthors = van Venrooij WJ, van Beers JJ, Pruijn GJ | s2cid = 11858403 | title = Anti-CCP antibodies: the past, the present and the future | journal = Nature Reviews. Rheumatology | volume = 7 | issue = 7 | pages = 391–398 | date = June 2011 | pmid = 21647203 | doi = 10.1038/nrrheum.2011.76 | hdl = 2066/91562 | hdl-access = free }}{{subscription required}}</ref> As with RF, ACPAs are many times present before symptoms have started.<ref name="McGraw Hill"/>

The by far most common clinical test for ACPAs is the anti-[[cyclic citrullinated peptide]] (anti CCP) ELISA. In 2008 a serological [[Point-of-care testing|point-of-care test]] for the early detection of RA combined the detection of RF and anti-MCV with a sensitivity of 72% and specificity of 99.7%.<ref>{{cite journal |vauthors=Renger F, Bang H, Fredenhagen G, et al |title=Anti-MCV Antibody Test for the Diagnosis of Rheumatoid Arthritis Using a POCT-Immunoassay |journal=American College of Rheumatology, 2008 Annual Scientific Meeting, Poster Presentation |url=http://acr.confex.com/acr/2008/webprogram/Paper2009.html |url-status=dead |archive-url=https://web.archive.org/web/20100527234743/http://acr.confex.com/acr/2008/webprogram/Paper2009.html |archive-date=2010-05-27 }}</ref>{{better source needed |date=July 2017}}<ref>{{cite journal | vauthors = Luime JJ, Colin EM, Hazes JM, Lubberts E | s2cid = 22283893 | title = Does anti-mutated citrullinated vimentin have additional value as a serological marker in the diagnostic and prognostic investigation of patients with rheumatoid arthritis? A systematic review | journal = Annals of the Rheumatic Diseases | volume = 69 | issue = 2 | pages = 337–344 | date = February 2010 | pmid = 19289382 | doi = 10.1136/ard.2008.103283 | url = http://ard.bmj.com/cgi/content/short/ard.2008.103283v1 }}{{subscription required}}</ref>

To improve the diagnostic capture rate in the early detection of patients with RA and to risk stratify these individuals, the rheumatology field continues to seek complementary markers to both RF and anti-CCP. 14-3-3η ([[YWHAH]]) is one such marker that complements RF and anti-CCP, along with other serological measures like [[C-reactive protein]]. In a systematic review, 14-3-3η has been described as a welcome addition to the rheumatology field. The authors indicate that the serum based 14-3-η marker is additive to the armamentarium of existing tools available to clinicians, and that there is adequate clinical evidence to support its clinical benefits.<ref>{{cite journal| vauthors = Abdelhafiz D, Kilborn S, Bukhari M | title = The role of 14-3-3 η as a biomarker in rheumatoid arthritis | journal = Rheumatology and Immunology Research. | date = June 2021 | volume = 2 | issue = 2 | pages = 87–90 | doi = 10.2478/rir-2021-0012 | pmid = 36465971 | pmc = 9524784 | s2cid = 238231522 }}</ref>

Other blood tests are usually done to differentiate from other causes of arthritis, like the [[erythrocyte sedimentation rate]] (ESR), C-reactive protein, [[full blood count]], [[kidney function]], [[liver enzyme]]s and other immunological tests (e.g., [[antinuclear antibody]]/ANA) are all performed at this stage. Elevated [[ferritin]] levels can reveal [[hemochromatosis]], a mimic of RA, or be a sign of [[Adult-onset Still's disease|Still's disease]], a seronegative, usually juvenile, variant of rheumatoid Arthritis.<ref>{{cite journal | vauthors = Barton JC, Barton JC | title = Autoimmune Conditions in 235 Hemochromatosis Probands with HFE C282Y Homozygosity and Their First-Degree Relatives | journal = Journal of Immunology Research | volume = 2015 | pages = 453046 | date = 2015 | pmid = 26504855 | pmc = 4609477 | doi = 10.1155/2015/453046 | doi-access = free }}</ref>