Editing Gout (section)

==Diagnosis==
{{Synovial fluid analysis}}
Gout may be diagnosed and treated without further investigations in someone with hyperuricemia and the classic acute arthritis of the base of the great toe (known as podagra). [[Synovial fluid]] analysis should be done if the diagnosis is in doubt.<ref name=Egg2007/><ref>{{cite journal|last1=Qaseem|first1=A|last2=McLean|first2=RM|last3=Starkey|first3=M|last4=Forciea|first4=MA|last5=Clinical Guidelines Committee of the American College of|first5=Physicians.|title=Diagnosis of Acute Gout: A Clinical Practice Guideline From the American College of Physicians|journal=Annals of Internal Medicine|date=3 January 2017|volume=166|issue=1|pages=52–57|pmid=27802479|doi=10.7326/m16-0569|doi-access=free}}</ref> Plain [[radiographs|X-rays]] are usually normal and are not useful for confirming a diagnosis of early gout.<ref name=Lancet2010/> They may show signs of chronic gout such as bone erosion.<ref name=CKS2019/>

===Synovial fluid===
A definitive diagnosis of gout is based upon the identification of [[monosodium urate crystals]] in [[synovial fluid]] or a [[tophus]].<ref name="Neogi2016"/> All synovial fluid samples obtained from undiagnosed inflamed joints by [[arthrocentesis]] should be examined for these crystals.<ref name=Lancet2010/> Under [[polarized light]] microscopy, they have a needle-like morphology and strong negative [[birefringence]]. This test is difficult to perform and requires a trained observer.<ref name="pmid18299687">{{cite journal |author=Schlesinger N |title=Diagnosis of gout |journal=Minerva Med. |volume=98 |issue=6 |pages=759–767 |year=2007 |pmid=18299687}}</ref> The fluid must be examined relatively soon after aspiration, as temperature and pH affect solubility.<ref name=Lancet2010/>

===Blood tests===
[[Hyperuricemia]] is a classic feature of gout, but nearly half of the time gout occurs without hyperuricemia and most people with raised uric acid levels never develop gout.<ref name=PM2010/><ref>{{cite journal | author = Sturrock R | title = Gout. Easy to misdiagnose | journal = [[British Medical Journal|BMJ]] | volume = 320 | issue = 7228 | pages = 132–133 | year = 2000 | pmid = 10634714| doi = 10.1136/bmj.320.7228.132 | pmc = 1128728}}</ref> Thus, the diagnostic utility of measuring uric acid levels is limited.<ref name=PM2010/> Hyperuricemia is defined as a [[blood plasma|plasma]] urate level greater than 420 μmol/L (7.0&nbsp;mg/dL) in males and 360 μmol/L (6.0&nbsp;mg/dL) in females.<ref>{{cite journal |vauthors=Sachs L, Batra KL, Zimmermann B |title=Medical implications of hyperuricemia |journal=Med Health R I |volume=92 |issue=11 |pages=353–355 |year=2009 |pmid=19999892}}</ref> Other blood tests commonly performed are [[white blood cell count]], [[electrolyte]]s, [[kidney function]] and [[erythrocyte sedimentation rate]] (ESR). However, both the white blood cells and ESR may be elevated due to gout in the absence of infection.<ref>{{cite journal |url=http://emedicine.medscape.com/article/329958-diagnosis |title=Gout: Differential Diagnoses & Workup – eMedicine Rheumatology |website=Medscape |url-status=live |archive-url=https://web.archive.org/web/20100725115050/http://emedicine.medscape.com/article/329958-diagnosis |archive-date=25 July 2010 |date=17 January 2019 }}</ref><ref>{{cite journal |url=http://emedicine.medscape.com/article/808628-diagnosis |title=Gout and Pseudogout: Differential Diagnoses & Workup – eMedicine Emergency Medicine |website=Medscape |url-status=live |archive-url=https://web.archive.org/web/20100311174806/http://emedicine.medscape.com/article/808628-diagnosis |archive-date=11 March 2010 |date=17 January 2019 }}</ref> A white blood cell count as high as 40.0×10<sup>9</sup>/l (40,000/mm<sup>3</sup>) has been documented.<ref name=Egg2007/>

===Differential diagnosis===
The most important [[differential diagnosis]] in gout is [[septic arthritis]].<ref name=Lancet2010/><ref name=PM2010/> This should be considered in those with signs of infection or those who do not improve with treatment.<ref name=PM2010/> To help with diagnosis, a synovial fluid [[Gram stain]] and culture may be performed.<ref name=PM2010/> Other conditions that can look similar include [[Calcium pyrophosphate dihydrate crystal deposition disease|CPPD]] (pseudogout), [[rheumatoid arthritis]], [[psoriatic arthritis]], [[palindromic rheumatism]], and [[reactive arthritis]].<ref name="Dalbeth2016"/><ref name=PM2010/> Gouty tophi, in particular when not located in a joint, can be mistaken for [[basal cell carcinoma]]<ref>{{cite journal |vauthors=Jordan DR, Belliveau MJ, Brownstein S, McEachren T, Kyrollos M |title=Medial canthal tophus |journal=Ophthal Plast Reconstr Surg |volume=24 |issue=5 |pages=403–404 |year=2008 |pmid=18806664 |doi=10.1097/IOP.0b013e3181837a31 }}</ref> or other [[neoplasm]]s.<ref>{{cite journal |vauthors=Sano K, Kohakura Y, Kimura K, Ozeki S |title=Atypical Triggering at the Wrist due to Intratendinous Infiltration of Tophaceous Gout |journal=Hand (N Y) |volume=4 |issue=1 |pages=78–80 |date=March 2009 |pmid=18780009 |doi=10.1007/s11552-008-9120-4 |pmc=2654956}}</ref>
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File:Light microscopy of a touch preparation of a gout tophus, showing urate crystals.jpg|Light microscopy of a touch preparation of a gout [[tophus]], showing needle-shaped crystals.
File:Birefringence microscopy of gout, annotated.jpg|Uric acid crystals in polarized light, showing negative [[birefringence]], with yellow color when aligned parallel to the axis of the red compensator, and blue when aligned perpendicularly to it.<ref>{{cite web |url=https://emedicine.medscape.com/article/329958-workup |title=Gout and Pseudogout Workup |first=Bruce M |last=Rothschild |website=Medscape |access-date=23 September 2020 |archive-date=8 October 2020 |archive-url=https://web.archive.org/web/20201008034412/https://emedicine.medscape.com/article/329958-workup |url-status=live }} Updated: Jun 30, 2020</ref>
File:Birefringence microscopy of pseudogout, annotated.jpg|In contrast, [[Calcium pyrophosphate dihydrate crystal deposition disease|CPPD]] (pseudogout) displays rhombus-shaped crystals with positive birefringence.
File:Gichtfuss im Roentgenbild 002.png|Gout on [[X-rays]] of a left foot in the metatarsal-phalangeal joint of the big toe. Note also the soft tissue swelling at the lateral border of the foot.
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