Medical test

For sociological tests, see laboratory studies.For laboratory test, see blood test.Medical tests can be classified by their purposes, the most common of which are diagnosis, screening and evaluation.Tests performed in a physical examination are usually aimed at detecting a symptom or 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 separate section below.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.Some medical testing procedures have associated health risks, and even require general anesthesia, such as the mediastinoscopy. Other tests, such as the blood test or pap smear have little to no direct risks. Medical tests may also have 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 physicians, physician assistants, and nurse practitioners) prescribing any test for further information.Each test has its own indications and contraindications. An indication is a valid medical reason to perform the test. A contraindication is a valid medical reason to reject 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).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 '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.The QUADAS-2 revision is available.