Editing Plague (disease) (section)

== Diagnosis ==
Symptoms of plague are usually non-specific and to definitively diagnose plague, laboratory testing is required.<ref name=":0" /> ''Y. pestis'' can be identified through both a microscope and by culturing a sample and this is used as a reference standard to confirm that a person has a case of plague.<ref name=":0" /> The sample can be obtained from the blood, mucus ([[sputum]]), or aspirate extracted from inflamed lymph nodes ([[bubo]]es).<ref name=":0" /> If a person is administered antibiotics before a sample is taken or if there is a delay in transporting the person's sample to a laboratory and/or a poorly stored sample, there is a possibility for [[False positives and false negatives|false negative]] results.<ref name=":0" />

[[Polymerase chain reaction]] (PCR) may also be used to diagnose plague, by detecting the presence of bacterial genes such as the ''pla'' gene (plasmogen activator) and ''caf1'' gene, (F1 capsule antigen).<ref name=":0" /> PCR testing requires a very small sample and is effective for both alive and dead bacteria.<ref name=":0" /> For this reason, if a person receives antibiotics before a sample is collected for laboratory testing, they may have a false negative culture and a positive PCR result.<ref name=":0" />

Blood tests to detect antibodies against ''Y. pestis'' can also be used to diagnose plague, however, this requires taking blood samples at different periods to detect differences between the acute and convalescent phases of F1 antibody titres.<ref name=":0" />

In 2020, a study about rapid diagnostic tests that detect the F1 capsule antigen (F1RDT) by sampling sputum or bubo aspirate was released.<ref name=":0" /> Results show rapid diagnostic F1RDT test can be used for people who have suspected pneumonic and bubonic plague but cannot be used in asymptomatic people. F1RDT may be useful in providing a fast result for prompt treatment and fast public health response as studies suggest that F1RDT is highly sensitive for both pneumonic and bubonic plague. However, when using the rapid test, both positive and negative results need to be confirmed to establish or reject the diagnosis of a confirmed case of plague and the test result needs to be interpreted within the epidemiological context as study findings indicate that although 40 out of 40 people who had the plague in a population of 1000 were correctly diagnosed, 317 people were diagnosed falsely as positive.<ref name=":0" /><ref>{{Cite journal |last1=Burch |first1=Jane |last2=Bhat |first2=Smitha |date=2021 |title=What is the accuracy of the rapid diagnostic test based on the antigen F1 (F1RDT) for the diagnosis of plague? |url=https://doi.org//10.1002/cca.3217 |journal=Cochrane Clinical Answers|doi=10.1002/cca.3217 |s2cid=234804227 }}</ref><ref>{{Cite book |title=WHO Guidelines for Plague Management |publisher=World Health Organization |year=2021 |pages=1–19}}</ref>