Diagnostic test

A diagnostic test is any kind of medical procedure performed to aid in the diagnosis or detection of disease. For example:
 * to diagnose diseases
 * to measure the progress or recovery from disease
 * to confirm that a person is free from disease

A drug test can be a specific medical test to acertain the presence of a certain drug in the body (for example, in drug addicts).

Overview
Some medical tests are parts of a simple physical examination which require only simple tools in the hands of a skilled practitioner, and can be performed in an office environment. Some other tests require elaborate equipment used by medical technologists or the use of a sterile operating theatre environment.

Some tests require samples of tissue or body fluids to be sent off to a pathology lab for further analysis. Some simple chemical tests, such as urine pH, can be measured directly in the doctor's office.

Most medical tests are conducted on the living; however, some of these tests can also be carried out on a dead person as part of an autopsy.

Medical tests can be classified into three categories:
 * invasive
 * minimally invasive
 * non-invasive

Properties
The result of a test 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).

Bayesian probability and performance metrics
Other characteristics of tests include:
 * sensitivity
 * specificity
 * positive predictive value
 * negative predictive value
 * false positive
 * false negative

Consulting room tests

 * auscultation, including listening with a stethoscope
 * weighing, and measuring height and girth
 * measuring blood pressure
 * taking the patient's pulse
 * breath tests
 * reflex tests
 * eye examination
 * ophthalmoscopy
 * hearing test
 * digital rectal examination
 * vaginal examination

More invasive examinations requiring sterile procedures

 * biopsies
 * lumbar puncture

Requiring laboratory analysis

 * urine tests
 * stool samples
 * saliva samples
 * hair samples
 * blood tests
 * ESR
 * CBC (complete blood count)
 * CMP (comprehensive metabolic panel)
 * blood gas monitor
 * DNA tests

Requiring microscopy

 * Pap smears

Requiring elaborate medical equipment

 * X-rays
 * barium enema
 * intravenous pyelogram (IVP test)
 * ultrasound scans
 * electrocardiogram (EKG)
 * electroencephalogram (EEG)
 * computer aided tomography scans
 * positron emission tomography (PET)
 * magnetic resonance imaging (MRI)
 * functional MRI
 * endoscopy
 * colonoscopy
 * cystoscopy
 * sigmoidoscopy
 * colposcopy

Psychological effects of diagnostic tests
Medical tests can have value when results are abnormal by explaining to a patient the cause of their symptoms. In addition, normal test results can have value by reassuring patients that serious illness is not present and even reduce the rates of subsequent symptoms. Understanding the meaning of a normal test in advance of learning the test results may also reduce the rates of subsequent symptoms.

Lack of adequate education about the meaning of test results (especially relevant to tests that may have incidental and unimportant findings) may cause an increase in symptoms. In addition, the possible benefits must be weighed against the costs of unnecessary tests and resulting unnecessary follow-up and possibly even unnecessary treatment of incidental findings.