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{{Short description|Medical procedure}}
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|  Name        = Medical test
|  Image       = X-ray by Wilhelm Röntgen of Albert von Kölliker's hand - 18960123-02.jpg
|  Caption     = [[X-ray]] of a hand. X-rays are a common medical test.
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|  MeshID      = D019937
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A '''medical test''' is a  [[medical procedure]] performed to [[screening (medicine)|detect]], [[medical diagnosis|diagnose]], or [[monitoring (medicine)|monitor]] diseases, disease processes, susceptibility, or to determine a course of treatment. Medical tests such as, physical and visual exams, [[diagnostic imaging]], genetic testing, chemical and cellular analysis, relating to [[clinical chemistry]] and [[molecular diagnostics]], are typically performed in a [[Medical laboratory|medical setting]].

==Types of tests ==

===By purpose===
Medical tests can be classified by their purposes, including diagnosis, screening or monitoring.

====Diagnostic====
[[Image:Lung scintigraphy keosys.JPG|thumb|Lung [[scintigraphy]] evaluating lung cancer]]
A diagnostic test is a procedure performed to confirm or determine the presence of disease in an individual suspected of having a disease, usually following the report of symptoms, or based on other medical test results.<ref name="anc">{{cite journal |vauthors=Al-Gwaiz LA, Babay HH |title=The diagnostic value of absolute neutrophil count, band count and morphological changes of neutrophils in predicting bacterial infections |journal=Med Princ Pract |volume=16 |issue=5 |pages=344–347 |year=2007 |pmid=17709921 |doi=10.1159/000104806 |doi-access=free }}</ref><ref>[http://www.health.harvard.edu/diagnostic-tests/ Harvard.edu] {{Webarchive|url=https://web.archive.org/web/20141223084541/http://www.health.harvard.edu/diagnostic-tests/ |date=2014-12-23 }}<br>Guide to Diagnostic Tests from Harvard Health</ref> This includes [[posthumous diagnosis]]. Examples of such tests are:
* Using [[nuclear medicine]] to examine a patient suspected of having a [[lymphoma]].
* Measuring the [[blood sugar]] in a person suspected of having [[diabetes mellitus]] after periods of increased [[urination]].
* Taking a [[complete blood count]] of an individual experiencing a high [[fever]] to check for a [[bacterial infection]].<ref name="anc" />
* Monitoring [[electrocardiogram]] readings on a patient with [[chest pain]] to diagnose or determine any [[heart]] irregularities.<ref>{{Cite web |url=http://www.health.harvard.edu/a_to_z/electrocardiogram-ekg |title=Harvard.edu |access-date=2016-11-07 |archive-date=2017-06-18 |archive-url=https://web.archive.org/web/20170618191136/http://www.health.harvard.edu/a_to_z/electrocardiogram-ekg |url-status=dead }}</ref>

====Screening====
{{Main|Screening (medicine)}}
[[screening (medicine)|Screening]] refers to a medical test or series of tests used to detect or predict the presence of disease in at-risk individuals within a defined group such as a population, family, or workforce.<ref>{{cite journal |vauthors=Ratcliffe JM, Halperin WE, Frazier TM, Sundin DS, Delaney L, Hornung RW |title=The prevalence of screening: a report from the National Institute of Occupational Safety and the Health National Occupational Hazard Survey |journal=Journal of Occupational Medicine |volume=28 |issue=10 |pages=906–912 |year=1986 |pmid=3021937 |doi=10.1097/00043764-198610000-00003 |url=https://zenodo.org/record/1234830 |access-date=2019-09-16 |archive-date=2021-10-20 |archive-url=https://web.archive.org/web/20211020044449/https://zenodo.org/record/1234830 |url-status=live }}</ref><ref>[https://www.osha.gov/SLTC/medicalsurveillance/screening.html Osha.gov] {{Webarchive|url=https://web.archive.org/web/20200810085338/https://www.osha.gov/SLTC/medicalsurveillance/screening.html |date=2020-08-10 }}<br>
US Dept. of Labor – Occupational Safety and Health Admin.</ref> Screenings may be performed to monitor disease prevalence, manage epidemiology, aid in prevention, or strictly for statistical purposes.<ref>{{cite journal |vauthors=Murthy LI, Halperin WE |title=Medical Screening and Biological Monitoring: A guide to the literature for physicians |journal=Journal of Occupational and Environmental Medicine |volume=37 |issue=2 |pages=170–184 |year=1995 |pmid=7655958 |doi=10.1097/00043764-199502000-00016 |s2cid=24916505 |url=https://zenodo.org/record/1234834 |access-date=2020-09-08 |archive-date=2021-10-20 |archive-url=https://web.archive.org/web/20211020044449/https://zenodo.org/record/1234834 |url-status=live }}</ref>

Examples of screenings include measuring the level of [[Thyroid-stimulating hormone|TSH]] in the [[blood]] of a newborn [[infant]] as part of [[newborn screening]] for [[congenital hypothyroidism]],<ref>{{cite journal |vauthors=Moltz KC, Postellon DC |title=Congenital hypothyroidism and mental development |journal=[[Comprehensive Therapy]] |volume=20 |issue=6 |pages=342–346 |year=1994 |pmid=8062543 }}</ref> checking for [[Lung cancer]] in non-smoking individuals who are exposed to [[Passive smoke|second-hand smoke]] in an unregulated working environment, and [[Pap test|Pap smear]] screening for prevention or early detection of [[cervical cancer]].{{citation needed|date=May 2022}}

====Monitoring====
{{Main|Monitoring (medicine)}}
Some medical tests are used to [[monitoring (medicine)|monitor]] the progress of, or response to [[therapy|medical treatment]].

===By method===
Most test methods can be classified into one of the following broad groups:
* Patient observations, which may be photographed or recorded
* Questions asked when taking an individual's [[medical history]]
* Tests performed in a [[physical examination]]
* [[Radiologic]] tests, in which, for example, [[x-rays]] are used to form an image of a body target. These tests often involve administration of a [[Contrast medium|contrast agent]].
* '''In vivo diagnostics''' which test in the body, such as:
** [[Pressure measurement|Manometry]]<ref>[http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-17-25-22423 OSA | Design of a high-sensor count fibre optic manometry catheter for in-vivo colonic diagnostics<!-- Bot generated title -->]</ref>
** Administering a diagnostic agent and measuring the body's response, as in the [[gluten challenge test]], [[contraction stress test]], [[bronchial challenge test]], [[oral food challenge]], or the [[ACTH stimulation test]].
* '''{{Vanchor|In vitro diagnostics}}''' which test a sample of tissue or bodily fluids,<ref>{{Cite web |url=http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:1998:331:0001:0037:EN:PDF |title=Directive 98/79/CE on in vitro diagnostic medical devices |access-date=2013-10-10 |archive-date=2021-10-21 |archive-url=https://web.archive.org/web/20211021233806/https://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:1998:331:0001:0037:EN:PDF |url-status=live }}</ref><ref>{{Cite web | url=http://www.edma-ivd.be/index.php?id=6 | title=In Vitro Diagnostic (IVD) tests |website = European Diagnostic Manufacturers Association|archive-url = https://web.archive.org/web/20090423083644/http://www.edma-ivd.be/index.php?id=6 |archive-date = 23 April 2009}}</ref> such as:
** [[Circulating tumor cell|Liquid biopsy]]
** [[Microbiological culture|Microbiological culturing]], which determines the presence or absence of microbes in a sample from the body, and usually targeted at detecting [[pathogenic bacteria]].
** [[Genetic testing]]
** [[Blood sugar level]]<ref>{{cite web|url = http://www.labtestsonline.org.uk/understanding/analytes/glucose/tab/test|title = Glucose Tests|website = Lab Tests Online UK|date = 14 November 2019|access-date = 10 October 2013|archive-date = 11 December 2011|archive-url = https://web.archive.org/web/20111211155857/http://www.labtestsonline.org.uk/understanding/analytes/glucose/tab/test|url-status = live}}</ref>
** Liver function testing<ref name="labtestsonline.org.uk">{{cite web|url = http://www.labtestsonline.org.uk/understanding/analytes/liver-panel/|title = Liver Function Tests|website = Lab Tests Online UK|date = 10 January 2020|access-date = 10 October 2013|archive-date = 5 December 2011|archive-url = https://web.archive.org/web/20111205115303/http://www.labtestsonline.org.uk/understanding/analytes/liver-panel/|url-status = live}}</ref>
** [[Calcium]] testing<ref name="labtestsonline.org.uk"/>
** Testing for electrolytes in the blood, such as [[sodium]], [[potassium]], [[creatinine]], and [[urea]]<ref>{{cite web |url = http://www.labtestsonline.org.uk/understanding/analytes/lytes |title = Electrolytes and Anion Gap |website = Lab Tests Online UK |date = 9 October 2019 |access-date = 10 October 2013 |archive-date = 27 November 2011 |archive-url = https://web.archive.org/web/20111127214347/http://www.labtestsonline.org.uk/understanding/analytes/lytes |url-status = live }}</ref>

===By sample location===
In vitro tests can be classified according to the location of the sample being tested, including:
* [[Blood test]]s
* [[Urinalysis|Urine tests]], including naked eye exam of the urine
* [[Stool test]]s, including naked eye exam of the feces
* [[Sputum]] ([[phlegm]]), including naked eye exam of the sputum

==Accuracy and precision==
{{Main|Accuracy and precision}}
* '''Accuracy''' of a laboratory test is its correspondence with the true value. Accuracy is maximized by calibrating laboratory equipment with reference material and by participating in external quality control programs.
* '''Precision''' of a test is its reproducibility when it is repeated on the same sample. An imprecise test yields widely varying results on repeated measurement. Precision is monitored in laboratory by using control material.

==Detection and quantification==
Tests performed in a [[physical examination]] are usually aimed at detecting a [[symptom]] or [[Medical sign|sign]], and in these cases, a test that detects a symptom or sign is designated a [[positive test]], and a test that indicated absence of a symptom or sign is designated a negative test, as further detailed in a separate section below.A quantification of a target substance, a cell type or another specific entity is a common output of, for example, most [[blood test]]s. This is not only answering ''if'' a target entity is present or absent, but also ''how much'' is present. In blood tests, the quantification is relatively well specified, such as given in [[mass concentration (chemistry)|mass concentration]], while most other tests may be quantifications as well although less specified, such as a sign of being "very [[Pallor|pale]]" rather than "slightly pale". Similarly, radiologic images are technically quantifications of radiologic opacity of tissues.{{citation needed|date=May 2022}}

Especially in the taking of a [[medical history]], there is no clear limit between a detecting or quantifying test versus rather ''descriptive'' information of an individual. For example, questions regarding the occupation or social life of an individual may be regarded as tests that can be regarded as positive or negative for the presence of various risk factors, or they may be regarded as "merely" descriptive, although the latter may be at least as clinically important.{{citation needed|date=May 2022}}

===Positive or negative===
{{Further|Positive and negative predictive values|False positives and false negatives}}
The result of a test aimed at detection of an entity may be '''positive''' or '''negative''': this has nothing to do with a bad [[prognosis]], but rather means that the test worked or not, and a certain parameter that was evaluated was present or not. For example, a negative [[screening test]] for [[breast cancer]] means that no sign of breast cancer could be found (which is in fact very positive for the patient).{{Citation needed|date=February 2020}}

The classification of tests into either positive or negative gives a [[binary classification]], with resultant ability to perform [[bayesian probability]] and performance metrics of tests, including calculations of [[sensitivity and specificity]].{{Citation needed|date=February 2020}}

===Continuous values===
Tests whose results are of continuous values, such as most [[blood values]], can be interpreted as they are, or they can be [[Artificially binary value|converted to a binary ones]] by defining a [[cutoff (reference value)|cutoff value]], with test results being designated as positive or negative depending on whether the resultant value is higher or lower than the cutoff.

==Interpretation==
{{Further|Pre- and post-test probability}}
In the finding of a ''[[pathognomonic]]'' sign or symptom it is almost certain that the target condition is present, and in the absence of finding a ''[[sine qua non]]'' sign or symptom it is almost certain that the target condition is absent. In reality, however, the subjective probability of the presence of a condition is never exactly 100% or 0%, so tests are rather aimed at estimating a [[post-test probability]] of a condition or other entity.

Most diagnostic tests basically use a [[reference group]] to establish performance data such as [[predictive values]], [[likelihood ratios in diagnostic testing|likelihood ratios]] and [[relative risk]]s, which are then used to interpret the post-test probability for an individual.

In monitoring tests of an individual, the test results from previous tests on that individual may be used as a reference to interpret subsequent tests.

==Risks==
Some medical testing procedures have associated health risks, and even require [[general anesthesia]], such as the [[mediastinoscopy]].<ref>{{cite web|publisher = Harvard.edu|title = Mediastinoscopy|website = Harvard Health|url = http://www.health.harvard.edu/diagnostic-tests/mediastinoscopy.htm |date = October 2016|url-access = subscription |archive-date = 6 October 2014|archive-url = https://web.archive.org/web/20141006072813/http://www.health.harvard.edu/diagnostic-tests/mediastinoscopy.htm }}</ref> Other tests, such as the [[blood test]] or [[pap smear]] have little to no direct risks.<ref>{{citation|url=http://www.health.harvard.edu/diagnostic-tests/pap-smear.htm|title=Diagnostic Tests > Pap Smear |publisher=[[Harvard University]]|archive-url=https://web.archive.org/web/20070608072504/http://www.health.harvard.edu/diagnostic-tests/pap-smear.htm|archive-date=June 8, 2007}}</ref> Medical tests may also have [[Screening (medicine)#Adverse effects of screening|indirect risks]], such as the stress of testing, and riskier tests may be required as follow-up for a (potentially) [[false positive]] test result. Consult the health care provider (including [[physician]]s, [[physician assistant]]s, and [[nurse practitioner]]s) prescribing any test for further information.

==Indications==
Each test has its own [[Indication (medicine)|indication]]s and contraindications.  An ''indication'' is a valid medical reason to perform the test.  A ''contraindication'' is a valid medical reason not to perform the test.  For example, a basic [[cholesterol test]] may be ''indicated'' (medically appropriate) for a middle-aged person.  However, if the same test was performed on that person very recently, then the existence of the previous test is a contraindication for the test (a medically valid reason to not perform it).

[[Information bias (psychology)|Information bias]] is the [[cognitive bias]] that causes healthcare providers to order tests that produce information that they do not realistically expect or intend to use for the purpose of making a medical decision.  Medical tests are indicated when the information they produce will be used.  For example, a screening mammogram is not indicated (not medically appropriate) for a woman who is dying, because even if breast cancer is found, she will die before any cancer treatment could begin.

In a simplified fashion, how much a test is indicated for an individual depends largely on its ''net benefit'' for that individual.  Tests are chosen when the expected benefit is greater than the expected harm.  The net benefit may roughly be estimated by:<ref>{{cite web|url=https://patholines.org/Clinical_pathology|title=Clinical pathology|author=Mikael Häggström, M.D.|website=Patholines.org|accessdate=2024-02-15}}</ref>

<math> b_n = \Delta p \times r_i \times ( b_i - h_i ) - h_t</math>

, where:
* ''b<sub>n</sub>'' is the net benefit of performing a test
* ''Λp'' is the absolute difference between [[pre- and posttest probability]] of conditions (such as diseases) that the test is expected to achieve. A major factor for such an absolute difference is the power of the test itself, such as can be described in terms of, for example, [[sensitivity and specificity]] or [[Likelihood ratios in diagnostic testing|likelihood ratio]]. Another factor is the pre-test probability, with a lower pre-test probability resulting in a lower absolute difference, with the consequence that even very powerful tests achieve a low absolute difference for very unlikely conditions in an individual (such as [[rare disease]]s in the absence of any other indicating sign), but on the other hand, that even tests with low power can make a great difference for highly suspected conditions. The probabilities in this sense may also need to be considered in context of conditions that are not primary targets of the test, such as [[Differential diagnosis#profile-relative probability|profile-relative probabilities in a differential diagnostic procedure]].
* ''r<sub>i</sub>'' is the rate of how much ''probability differences'' are expected to result in ''changes in interventions'' (such as a change from "no treatment" to "administration of low-dose medical treatment"). For example, if the only expected effect of a medical test is to make one disease more likely compared to another, but the two diseases have the same treatment (or neither can be treated), then, this factor is very low and the test is probably without value for the individual in this aspect.
* ''b<sub>i</sub>'' is the benefit of ''changes in interventions'' for the individual
* ''h<sub>i</sub>'' is the harm of ''changes in interventions'' for the individual, such as [[side effects]] of medical treatment
* ''h<sub>t</sub>'' is the harm caused by the test itself.

Some additional factors that influence a decision whether a medical test should be performed or not included: cost of the test, availability of additional tests, potential interference with subsequent test (such as an [[abdominal palpation]] potentially inducing intestinal activity whose sounds interfere with a subsequent [[abdominal auscultation]]), time taken for the test or other practical or administrative aspects. The possible benefits of a diagnostic test may also be weighed against the costs of unnecessary tests and resulting unnecessary follow-up and possibly even unnecessary treatment of incidental findings.<ref name="pmid12783911">{{cite journal |vauthors=Jarvik J, Hollingworth W, Martin B, Emerson S, Gray D, Overman S, Robinson D, Staiger T, Wessbecher F, Sullivan S, Kreuter W, Deyo R |title=Rapid magnetic resonance imaging vs radiographs for patients with low back pain: a randomized controlled trial |journal=JAMA |volume=289 |issue=21 |pages=2810–8 |year=2003 |pmid=12783911 |doi=10.1001/jama.289.21.2810|doi-access= |s2cid=22897506 }}</ref>

In some cases, tests being performed are expected to have no benefit for the individual being tested.  Instead, the results may be useful for the establishment of statistics in order to improve health care for other individuals. Patients may give [[informed consent]] to undergo medical tests that will benefit other people.

==Patient expectations==

In addition to considerations of the nature of medical testing noted above, other realities can lead to misconceptions and unjustified expectations among patients. These include: Different labs have different normal reference ranges; slightly different values will result from repeating a test; "normal" is defined by a spectrum along a bell curve resulting from the testing of a population, not by "rational, science-based, physiological principles"; sometimes tests are used in the hope of turning something up to give the doctor a clue as to the nature of a given condition; and imaging tests are subject to fallible human interpretation and can show [[Incidental imaging finding|"incidentalomas"]], most of which "are benign, will never cause symptoms, and do not require further evaluation," although clinicians are developing guidelines for deciding when to pursue diagnoses of incidentalomas.<ref>{{cite journal |last1=Hall |first1=Harriet |author-link1=Harriet Hall |title=Too Many Medical Tests |journal=[[Skeptical Inquirer]] |date=2019 |volume=43 |issue=3 |pages=25–27}}</ref>

==Standard for the reporting and assessment==
The QUADAS-2 revision is available.<ref>{{Cite journal
 |doi=10.7326/0003-4819-155-8-201110180-00009
 |pmid=22007046
 |volume=155
 |issue=8
 |pages=529–36
 |vauthors=Whiting PF, Rutjes AW, Westwood ME, Mallett S, Deeks JJ, Reitsma JB, Leeflang MM, Sterne JA, Bossuyt PM
 |collaboration=QUADAS-2 Group
 |title=QUADAS-2: a revised tool for the quality assessment of diagnostic accuracy studies
 |journal=Annals of Internal Medicine
 |date=October 2011
|doi-access=
 }}</ref>

==List of medical tests==
{{main|list of medical tests}}

==See also==
{{col div|colwidth=40em}}
* [[Blood culture]]
* [[Chemical test]]
* [[Gold standard (test)]]
* [[Medical sign]]
* [[Molecular diagnostics]]
* [[Nailbed assessment]]
* [[Test panel]]
* [[Point-of-care testing]]
* [[Regulation (EU) 2017/746|EU IVD Regulation]]
{{colend}}

==References==
{{reflist|30em}}

==Further reading==
* {{cite book | vauthors = ((World Health Organization)) | title = First WHO Model List of Essential In Vitro Diagnostics | year = 2019 | publisher = World Health Organization | hdl = 10665/311567 | author-link = World Health Organization | location = Geneva | id = WHO Technical Report Series, No. 1017. License: CC BY-NC-SA 3.0 IGO | isbn = 978-92-4-121026-3 | issn = 0512-3054 }}
{{Medical imaging}}
{{Urine tests}}
{{Clinical biochemistry blood tests}}
{{Myeloid blood tests}}
{{CSF tests}}
{{Immunologic techniques and tests}}
{{Transfusion medicine}}
{{Infectious blood tests}}
{{Pathology}}
{{Electrodiagnosis}}
{{Authority control}}
{{Portal bar | Medicine}}

[[Category:Medical tests| ]]
[[Category:Pathology]]