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 ascertain the presence of a certain drug in the body (for example, in drug addicts).

Contents 1 Overview 2 Test Characteristics 2.1 Properties 2.2 Bayesian probability and performance metrics 3 Types of medical tests 3.1 Consulting room tests 3.2 More invasive examinations requiring sterile procedures 3.3 Requiring laboratory analysis 3.4 Requiring microscopy 3.5 Requiring elaborate medical equipment 4 Psychological effects of diagnostic tests 5 See also 6 References

[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:

• invasive
• minimally invasive
• non-invasive

[edit] Test Characteristics

• Accuracy of a laboratory test 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 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
  • ophthalmoscopy
• hearing test
• digital rectal examination
• vaginal examination

[edit] More invasive examinations requiring sterile procedures

• biopsies
• lumbar puncture

[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

• Pap smears

[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
  • positron emission tomography (PET)
  • magnetic resonance imaging (MRI)
    • functional MRI
• endoscopy
  • colonoscopy
  • cystoscopy
  • sigmoidoscopy
  • colposcopy
• blood test

[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

• Medical diagnosis
• Medical record
• Physical examination

[edit] References