Diagnostic test
From Wikipedia, the free encyclopedia
A diagnostic test is any kind of medical test 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).
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[edit] 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.
The validity of diagnostic test results produced in each laboratory is entirely dependent on the measures employed before, during, and after each assay. Consistency in the production of good results requires an overall program that includes quality assurance, quality control, and quality assessment.
Medical tests can be classified into three categories:
[edit] Test Characteristics
Accuracy Accuracy of a laboratory tests is its correspondence with the true value. Accuracy is maximized by calibrating laboratory equipment with reference material and by participation in external quality control programs.
Precision The precision is a measure of tests reproducibility when repeated on the same sample. An imprecise test is one that yield widely varying results on repeated measurement. The precision is monitored in laboratory by using control material.
[edit] 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).
[edit] Bayesian probability and performance metrics
Other characteristics of tests include:
- sensitivity
- specificity
- positive predictive value
- negative predictive value
- false positive
- false negative
[edit] Types of medical tests
[edit] 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
- hearing test
- digital rectal examination
- vaginal examination
[edit] More invasive examinations requiring sterile procedures
[edit] Requiring laboratory analysis
- Urine tests
- Stool tests
- Saliva tests
- Hair tests
- Blood tests
- Erythrocyte sedimentation rate (ESR)
- Complete blood count (CBC)
- Comprehensive metabolic panel (CMP)
- Arterial blood gas (ABG)
- DNA tests
[edit] Requiring microscopy
[edit] Requiring elaborate medical equipment
- X-rays
- barium enema
- intravenous pyelogram (IVP test)
- ultrasound scans
- electrocardiogram (ECG or EKG)
- electroencephalogram (EEG)
- computer aided tomography (CAT) scans
- endoscopy
[edit] Psychological effects of diagnostic tests
Medical tests can have value when results are abnormal by explaining to a patient the cause of their symptoms[1]. 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 [2]. Understanding the meaning of a normal test in advance of learning the test results may also reduce the rates of subsequent symptoms [3].
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 [4]. 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 [5].
[edit] See also
[edit] References
- ^ Ward B, Wu W, Richter J, Hackshaw B, Castell D (1987). "Long-term follow-up of symptomatic status of patients with noncardiac chest pain: is diagnosis of esophageal etiology helpful?". Am J Gastroenterol 82 (3): 215-8. PMID 3826028.
- ^ Sox H, Margulies I, Sox C (1981). "Psychologically mediated effects of diagnostic tests". Ann Intern Med 95 (6): 680-5. PMID 7305144.
- ^ Petrie K, Müller J, Schirmbeck F, Donkin L, Broadbent E, Ellis C, Gamble G, Rief W (2007). "Effect of providing information about normal test results on patients' reassurance: randomised controlled trial". BMJ 334: 352. doi:. PMID 17259186.
- ^ Kendrick D, Fielding K, Bentley E, Kerslake R, Miller P, Pringle M (2001). "Radiography of the lumbar spine in primary care patients with low back pain: randomised controlled trial". BMJ 322 (7283): 400-5. doi:. PMID 11179160.
- ^ Jarvik J, Hollingworth W, Martin B, Emerson S, Gray D, Overman S, Robinson D, Staiger T, Wessbecher F, Sullivan S, Kreuter W, Deyo R (2003). "Rapid magnetic resonance imaging vs radiographs for patients with low back pain: a randomized controlled trial". JAMA 289 (21): 2810-8. doi:. PMID 12783911.
