Editing Chagas disease (section)

==Diagnosis==
[[File:T. cruzi trypomastigotes in peripheral blood smear.jpg|thumb|left|alt=Four T. cruzi parasites surrounded by red blood cells. Undulating membranes, flagella, and kinetoplasts are visible.|''T. cruzi'' trypomastigotes seen in a [[blood smear]]]]
The presence of ''T. cruzi'' in the blood is diagnostic of Chagas disease. During the acute phase of infection, it can be detected by [[microscope|microscopic]] examination of fresh [[anticoagulant|anticoagulate]]d blood, or its [[buffy coat]], for motile parasites; or by preparation of thin and thick [[blood smear]]s stained with [[Giemsa stain|Giemsa]], for direct visualization of parasites.<ref name="Bern2015"/><ref name=Gua2019/> Blood smear examination detects parasites in 34–85% of cases. The [[Sensitivity (statistics)|sensitivity]] increases if techniques such as [[microhematocrit|microhematocrit centrifugation]] are used to concentrate the blood.<ref name="Molina2018"/> On microscopic examination of stained blood smears, {{nowrap|''T. cruzi''}} trypomastigotes appear as S or U-shaped organisms with a [[flagellum]] connected to the body by an undulating membrane. A [[Cell nucleus|nucleus]] and a smaller structure called a [[kinetoplast]] are visible inside the parasite's body; the kinetoplast of {{nowrap|''T. cruzi''}} is relatively large, which helps to distinguish it from other species of trypanosomes that infect humans.<ref name="Bain2015">{{cite book| vauthors= Bain BJ| title= Blood Cells: A Practical Guide|url= https://books.google.com/books?id=dckoCQAAQBAJ |date= 20 January 2015 |publisher= John Wiley & Sons |isbn= 978-1-118-81733-9 |pages= 165–7}}</ref>

Alternatively, ''T. cruzi'' DNA can be detected by [[polymerase chain reaction]] (PCR). In acute and congenital Chagas disease, PCR is more sensitive than microscopy,<ref name="Bern2019"/> and it is more reliable than antibody-based tests for the diagnosis of congenital disease because it is not affected by the transfer of antibodies against {{nowrap|''T. cruzi''}} from a mother to her baby ([[Passive immunity#Naturally acquired|passive immunity]]).<ref>{{Cite journal|vauthors= Schijman AG |date= August 2018 |title= Molecular diagnosis of Trypanosoma cruzi | journal= Acta Tropica | volume=184 |pages=59–66|doi= 10.1016/j.actatropica.2018.02.019|pmid= 29476727|hdl= 11336/79861|s2cid= 3513900 |hdl-access= free }}</ref> PCR is also used to monitor {{nowrap|''T. cruzi''}} levels in organ transplant recipients and immunosuppressed people, which allows infection or reactivation to be detected at an early stage.<ref name="Molina2018"/><ref name="Bern2015"/><ref name="Bern2019"/>

In chronic Chagas disease, the [[Parasitemia|concentration of parasites in the blood]] is too low to be reliably detected by microscopy or PCR,<ref name="Molina2018"/> so the diagnosis is usually made using [[Serology|serological]] tests, which detect [[immunoglobulin G]] antibodies against {{nowrap|''T. cruzi''}} in the blood.<ref name=Gua2019/> Two positive serology results, using different test methods, are required to confirm the diagnosis.<ref name="Bern2015"/> If the test results are inconclusive, additional testing methods such as [[Western blot]] can be used.<ref name="Molina2018"/>

Various [[rapid diagnostic test]]s for Chagas disease are available. These tests are easily transported and can be performed by people without special training.<ref name="Luquetti2019">{{cite book|vauthors=Luquetti AO, Schijman AG|title=Chagas Disease |chapter=Diagnosis of Chagas Disease |editor=Marcelo Altcheh J, Freilij H|url=https://books.google.com/books?id=WpyuDwAAQBAJ|series=Birkhäuser Advances in Infectious Diseases|date=9 September 2019|publisher=Springer Nature|location=Switzerland|isbn=978-3-030-00054-7|pages=141–58|doi=10.1007/978-3-030-00054-7_7|s2cid=203376369|issn=2504-3811}}</ref> They are useful for [[Screening (medicine)|screening]] large numbers of people and testing people who cannot access healthcare facilities, but their sensitivity is relatively low,<ref name="Molina2018"/> and it is recommended that a second method is used to confirm a positive result.<ref name="Luquetti2019"/><ref name="Gurtler2019">{{cite journal | vauthors = Angheben A, Buonfrate D, Cruciani M, et al| title = Rapid immunochromatographic tests for the diagnosis of chronic Chagas disease in at-risk populations: A systematic review and meta-analysis | journal = PLOS Neglected Tropical Diseases | volume = 13 | issue = 5 | pages = e0007271 | date = May 2019 | pmid = 31150377 | doi = 10.1371/journal.pntd.0007271 | pmc = 6561601 | doi-access = free }}</ref>

''T. cruzi'' parasites can be grown from blood samples by [[blood culture]], [[xenodiagnosis]], or by inoculating animals with the person's blood. In the blood culture method, the person's [[red blood cell]]s are separated from the [[Blood plasma|plasma]] and added to a specialized [[growth medium]] to encourage multiplication of the parasite. It can take up to six months to obtain the result. Xenodiagnosis involves feeding the blood to triatomine insects, and then examining their feces for the parasite 30 to 60 days later.<ref name="Luquetti2019"/> These methods are not routinely used, as they are slow and have low sensitivity.<ref name=emed>{{cite web |url=http://emedicine.medscape.com/article/214581-overview |title=Chagas disease (American Trypanosomiasis) |vauthors= Kirchhoff OV|date=26 April 2019 |publisher=[[eMedicine]] |access-date=8 April 2020 |url-status=live |archive-url=https://web.archive.org/web/20200312071301/https://emedicine.medscape.com/article/214581-overview|archive-date=12 March 2020}}</ref><ref name="Luquetti2019"/>