• Diagnostic test:
A procedure or instrument used in conjunction with observation of behaviour patterns, history , and clinical examination to help in establishing the presence, nature, and source of, or vulnerability to, a disorder, or to measure some specified characteristic of an individual or group. Physical specimens tested vary according to the nature of the investigation: examples include urine (e.g. for the presence of drugs), blood (e.g. for blood alcohol level), semen (e.g. for motility of spermatozoa), faeces (e.g. for the presence of parasites), amniotic fluid (e.g. for the presence of a heritable disorder in the fetus), and tissues (e.g. for the presence and activity of neoplastic cells).The methods of testing also vary and include biochemical, immunological, neurophysiological and histological examinations. Diagnostic imaging techniques include X-ray, computed tomography (CAT scan), positron emission tomography (PET), and magnetic resonance imaging (MRI). Psychological investigations may involve intelligence tests, personality tests, projective tests (such as the Rorschach ink blot test), and neuro-psychological batteries of tests to assess the type, location, and degree of any brain dysfunction and its behavioural expressions. See also: screening test

• Diagnostic instrument:
In general medical usage, any machine or instrument, and by extension-any clinical procedure or interview schedule used for the determination of an individual's medical condition or the nature of his or her illness. With respect to substance use and other behavioural disorders, the term refers principally to lists of questions oriented to diagnosis, including structured interview schedules that can be administered by trained lay interviewers. The Composite International Diagnostic Interview (CIDI) and the Diagnostic Interview Schedule (DIS) are examples of such schedules, which allow diagnosis of psychoactive substance use disorders as well as a range of other mental disorders. See also: screening test