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A differential diagnosis (sometimes abbreviated DDx, ddx, or ??) is a systematic method used to identify unknowns. This method, essentially a process of elimination
Process of elimination

The process of elimination is a basic logical tool to solve real world problems. By subsequently removing options that may be deemed impossible, illogical, or can be easily ruled out due to some sort of explicit understanding relative to the entire set of options, the pool of remaining possibilities grows smaller....
, is used by taxonomists
Taxonomy

Taxonomy is the practice and science of classification. The word comes from the Greek language ', taxis and ', nomos .Taxonomies, or taxonomic schemes, are composed of taxonomic units known as taxa , or kinds of things that are arranged frequently in a hierarchical structure....
 to identify living organisms, and by physicians and other qualified healthcare professionals to diagnose
Diagnosis

Diagnosis is the identification of the nature of anything, either by process of elimination or other analytical methods. Diagnosis is used in many different disciplines, with slightly different implementations on the application of logic and experience to determine the cause and effect relationships....
 the specific disease
Disease

A disease or medical condition is an abnormal condition of an organism that impairs bodily functions, associated with specific symptoms and Medical signs....
 in a patient
Patient

A patient is any person who receives medical attention, care, or Therapy. The person is most often illness or injured and in need of treatment by a physician or other Health care provider, although one who is visiting a physician for a routine check-up may also be viewed as a patient....
. Not all medical diagnoses are differential ones: some diagnoses merely name a set of signs and symptom
Symptom

A symptom is a departure from normal function or feeling which is noticed by a patient, indicating the presence of disease or abnormality. A symptom is subjective, observed by the patient, and not measured....
s that may have more than one possible cause, and some diagnoses are based on intuition
Intuition

Intuition has many related meanings, usually connected to the meaning "ability to sense or know immediately without reasoning", and is often regarded as a divine or prophetic power, including:...
 or estimations of likelihood.

Process
The term differential derives from the word difference: careful differential diagnosis involves first making a list of possible diagnoses, then attempting to remove diagnoses from the list until at most one diagnosis remains.






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A differential diagnosis (sometimes abbreviated DDx, ddx, or ??) is a systematic method used to identify unknowns. This method, essentially a process of elimination
Process of elimination

The process of elimination is a basic logical tool to solve real world problems. By subsequently removing options that may be deemed impossible, illogical, or can be easily ruled out due to some sort of explicit understanding relative to the entire set of options, the pool of remaining possibilities grows smaller....
, is used by taxonomists
Taxonomy

Taxonomy is the practice and science of classification. The word comes from the Greek language ', taxis and ', nomos .Taxonomies, or taxonomic schemes, are composed of taxonomic units known as taxa , or kinds of things that are arranged frequently in a hierarchical structure....
 to identify living organisms, and by physicians and other qualified healthcare professionals to diagnose
Diagnosis

Diagnosis is the identification of the nature of anything, either by process of elimination or other analytical methods. Diagnosis is used in many different disciplines, with slightly different implementations on the application of logic and experience to determine the cause and effect relationships....
 the specific disease
Disease

A disease or medical condition is an abnormal condition of an organism that impairs bodily functions, associated with specific symptoms and Medical signs....
 in a patient
Patient

A patient is any person who receives medical attention, care, or Therapy. The person is most often illness or injured and in need of treatment by a physician or other Health care provider, although one who is visiting a physician for a routine check-up may also be viewed as a patient....
. Not all medical diagnoses are differential ones: some diagnoses merely name a set of signs and symptom
Symptom

A symptom is a departure from normal function or feeling which is noticed by a patient, indicating the presence of disease or abnormality. A symptom is subjective, observed by the patient, and not measured....
s that may have more than one possible cause, and some diagnoses are based on intuition
Intuition

Intuition has many related meanings, usually connected to the meaning "ability to sense or know immediately without reasoning", and is often regarded as a divine or prophetic power, including:...
 or estimations of likelihood.

Process


The term differential derives from the word difference: careful differential diagnosis involves first making a list of possible diagnoses, then attempting to remove diagnoses from the list until at most one diagnosis remains. In some cases, there will remain no diagnosis; this suggests the physician has made an error, or that the true diagnosis is unknown to medicine. Removing diagnoses from the list is done by making observations and using tests that should have different results, depending on which diagnosis is correct.

Differential diagnosis is the process whereby a given condition or circumstance, called the presenting problem or chief complaint, is examined in terms of underlying causal factors and concurrent phenomena as discerned by appropriate disciplinary perspectives and according to several theoretical paradigms or frames of reference, and compared to known categories of pathology
Pathology

Pathology is the study and diagnosis of disease through examination of Organ , tissue , bodily fluids and whole bodies . The term also encompasses the related science study of disease processes, called General pathology....
 or exceptionality. Differential diagnosis allows the physician to:

  • more clearly understand the condition or circumstance
  • assess reasonable prognosis
    Prognosis

    Prognosis is a medicine term denoting the Physician's prediction of how a patient will progress, and whether there is a chance of recovery. This word is often used in medical reports dictating a physician's view on a case....
  • eliminate any imminently life-threatening conditions
  • plan treatment or intervention for the condition or circumstance
  • enable the patient and the family to integrate the condition or circumstance into their lives, until the condition or circumstance may be ameliorated, if possible.


If the patient's condition does not improve as anticipated when the treatment or therapy for the disease or disorder has been applied, the diagnosis must be reassessed.

The method of differential diagnosis was first suggested for use in the diagnosis of mental disorders by Emil Kraepelin
Emil Kraepelin

Emil Kraepelin was a Germany psychiatrist. The Encyclopedia of Psychology by H. J. Eysenck identifies him as the founder of contemporary scientific psychiatry, as well as of psychopharmacology and psychiatric genetics....
. It is more systematic than the old-fashioned method of diagnosis by gestalt
Gestalt

Die Gestalt is a German language word for form or shape. It is used in English to refer to a concept of 'wholeness' . Gestalt may also refer to:...
 (impression).

The method of differential diagnosis is based on the idea that one begins by first considering the statistically more probable diagnoses. Medical students are taught the adage, "When you hear hoofbeats in Texas, think horses, not zebras"; only after more probable diagnoses are ruled out should the somewhat less likely ones be considered.

It used to be that doctors ordered only particular blood tests, but now a full blood-chemistry profile is standard, which can speed up the process of diagnosis as well as uncover sub-clinical
Sub-clinical

Sub-clinical is a medical term referring to a disease process that has initiated but has not yet manifested symptoms.One example is sub-clinical hypothyroidism, where a patient will manifest none of the typical symptoms of hypothyroidism, and blood tests will show a normal triiodothyronine and thyroxine, but an elevated TSH--indicating that...
 conditions. With the advent of better radiological
Radiology

Radiology is the branch or speciality of medicine that deals with the study and application of imaging technology like x-ray and radiation to diagnosing and treating disease....
 studies like MRI and the wider use of nuclear medicine
Nuclear medicine

Nuclear medicine is a branch of medicine and medical imaging that uses radioactive isotopes in the diagnosis of disease. Nuclear medicine thus relies on the process of radioactive decay....
, it has become more likely that there will be unexpected findings that will be further studied, though such findings may not be supported by further investigation. They are a valuable tool, but not infallible; it still often takes a physicians' or medical team to track down either a more common illness with a rare presentation, or a rare illness with symptoms suggestive of many other conditions. Sometimes a definitive diagnosis might take years.

Differential diagnosis also refers simply to a list of the most common causes of a given symptom, or a list of disorders similar to a given disorder, or to such lists when they are annotated with advice on how to narrow the list down (the book French's Index of Differential Diagnosis ISBN 0340810475 is an example). Thus, a differential diagnosis in this sense is medical information specially organized to aid in diagnosis.

The professional Merck Manual of Diagnosis and Therapy
Merck Manual of Diagnosis and Therapy

The Merck Manual of Diagnosis and Therapy, often called simply The Merck Manual, is the world's best-selling medical textbook. First published in 1899, it is now in its 18th edition....
 has 11 index entries describing the topic as differential diagnosis. The topic is mentioned within the body of 125 other separate articles on various medical conditions.

Machine differential diagnosis

Machine differential diagnosis is the use of computer software
Computer software

Computer software, or just software is a general term used to describe a collection of computer programs, Algorithm and Software documentation that perform some tasks on a computer system....
 to partly or fully make a differential diagnosis. It may be regarded as an application of artificial intelligence.

Many studies demonstrate improvement of quality of care and reduction of medical errors by using such decision support systems. Some of these systems are designed for a specific medical problem such as Schizophrenia , Lyme disease or Ventilator Associated Pneumonia . Others such as Iliad, QMR and DiagnosisPro are designed to cover all major clinical and diagnostic findings to assist physicians with faster and more accurate diagnosis.

However, these tools all still require advanced medical skills, in order to rate the symptoms and choose additional tests to deduce the probabilities of different diagnoses. Thus, non-professionals still need to see a health care provider
Health care provider

A health care provider or health professional is an organization or person who delivers proper health care in a systematic way professionally to any individual in need of health care services....
 in order to get a proper diagnosis.

See also

  • List of medical symptoms
    List of medical symptoms

    Medical symptoms are complaints which indicate disease. They are noticed by the patient and cause people to go and see a health practitioner. It is rare that a person would visit a doctor and complain as follows: "Doctor, I have amaurosis fugax." They are more likely to complain of Blindness....
  • Medical sign
    Medical sign

    A medical sign is an Objectivity indication of some medical fact or characteristic that may be detected by a physician during a physical examination of a patient....


Dictionary definitions

  • "differential diagnosis." Merriam-Webster's Medical Dictionary. Merriam-Webster, Inc. 12 Aug. 2007. .
  • "differential diagnosis." The American Heritage Stedman's Medical Dictionary. Houghton Mifflin Company. 12 Aug. 2007. .
  • "differential diagnosis." Google search of the online .