Medical diagnosis (abbreviated as Ds or Dx on a chart) is the process of determining which disease or condition explains a person's symptoms and signs. It is most often referred to as diagnosis with the medical context being implicit. The information required for diagnosis is typically collected from a medical history and physical examination of the person seeking medical care. Often, one or more diagnostic procedures, such as diagnostic tests, are also done during the process.

Diagnosis is often challenging, because many signs and symptoms are nonspecific. For example, redness of the skin (erythema), by itself, is a sign of many disorders and thus doesn't tell the healthcare professional what is wrong. Thus differential diagnosis, in which several possible explanations are compared and contrasted, must be performed. This involves the correlation of various pieces of information followed by the recognition and differentiation of patterns. Occasionally the process is made easy by a sign or symptom (or a group of several) that is pathognomonic, or specific to a single disease.

Diagnosis is a major component of the procedure of a doctor's visit. From the point of view of statistics, the diagnostic procedure involves classification tests.

House is accepted to be the hospital's best diagnostician, and he is often thought to be one of the best at this task of any doctor in the world. However, most diagnoses are straightforward. House and his team work on cases where other doctors in the hospital are unable to make a definitive diagnosis. 

The 4 cornerstones of diagnostics are anatomy, physiology, pathology, and psychology.

History and etymologyEdit

The first recorded examples of medical diagnosis are found in the writings of Imhotep (2630-2611 BC) in ancient Egypt. A Babylonian medical textbook, the Diagnostic Handbook written by Esagil-kin-apli (about 1069-1046 BC), introduced the use of empiricism, logic and rationality in the diagnosis of an illness or disease. Traditional Chinese Medicine, as described in the Yellow Emperor's Inner Canon or Huangdi Neijing, specified four diagnostic methods: inspection, auscultation-olfaction, interrogation, and palpation. Hippocrates was known to make diagnoses by tasting his patients' urine and smelling their sweat.

The medical profession has approached the problem of diagnosis in different ways over the centuries since Hippocrates, and other great ancient physicians such as Galen and their approach to diagnosis influenced physicians well into the late nineteenth century. Often, the correct approach to diagnosis was discussed in philosophical terms and even medical establishments would have two competing schools of thought as to how diagnosis should be approached.

During the nineteenth century, the practice of medicine generally moved from that of having the physician merely provide the treatment the patient wanted to a more systematic approach that was used on a wider (and more socially varied) variety of patients that focused on the identification of new conditions and establishing a diagnosis. The development of pathology during this period of time clearly drove the philosophy that if a disease could be definitively determined during an autopsy, the same could be done while the patient was still alive. The combination of the diagnosis of living patients and the pathology of dead patients eventually led to the identification of hundreds of new distinct conditions during the period leading up to the twentieth century. However, this increase in diagnostic specificity came with a decline in the use of treatments (most of which, like bloodletting, turned out to be harmful). In many cases, the diagnosis was the end of the physician's involvement as nothing could be done for the patient at that point except for supportive care. It was only through the development of anesthetic in the mid-18th century, antibiotics in the mid-20th century and pharmacotherapy in the late 20th century that treatment once again came to the forefront of the practice of medicine.

Although the modern approach to diagnosis is completely empirical and attempts to follow the "hypothesis refinement" method, physicians have often agreed that intuition or "hunches" form at least part of the process, even in modern times. Much of this is merely a shortcut due to extensive experience in a particular field which leaves doctors unable to verbalize their reasoning process. However, even young doctors have "eureka" moments when a previously unconsidered diagnosis leaps to mind because it fits the patient's symptoms.

The plural of diagnosis is diagnoses. The verb is to diagnose, and a person who diagnoses is called a diagnostician. The word diagnosis is derived through Latin from the Ancient Greek word διάγνωσις from διαγιγνώσκειν, meaning "to discern, distinguish".

The word first entered English in the seventeenth century, but rather than denoting "distinguishing", had a meaning closer to "elucidate" - to give a name to a condition rather than distinguishing it from different conditions.

Medical diagnosis or the actual process of making a diagnosis is a cognitive process. A clinician uses several sources of data and puts the pieces of the puzzle together to make a diagnostic impression. The initial diagnostic impression can be a broad term describing a category of diseases (such as "infection") instead of a specific disease or condition. After the initial diagnostic impression, the clinician obtains follow up tests and procedures to get more data to support or reject the original diagnosis and will attempt to narrow it down to a more specific level. Diagnostic procedures are the specific tools that the clinicians use to narrow the diagnostic possibilities.

Diagnostic proceduresEdit

A diagnosis, in the sense of diagnostic procedure, can be regarded as an attempt at classification of an individual's condition into separate and distinct categories that allow medical decisions about treatment and prognosis to be made. Subsequently, a diagnostic opinion is often described in terms of a disease or other condition, but in the case of a wrong diagnosis, the individual's actual disease or condition is not the same as the individual's diagnosis.

A diagnostic procedure may be performed by various health care professionals such as a physician, physical therapist, optometrist, healthcare scientist, chiropractor, dentist, podiatrist, nurse practitioner, or physician assistant.

A diagnostic procedure (as well as the opinion reached thereby) does not necessarily involve elucidation of the etiology of the diseases or conditions of interest, that is, what caused the disease or condition. Such elucidation can be useful to optimize treatment, further specify the prognosis or prevent recurrence of the disease or condition in the future.

Some doctors use a "decision theory" approach based on an assessment at each stage of the physician's judgment, what information will be obtained by further testing, the possible side effects of tests or treatments, and the value to either the physician or the patient that can be expected. This approach is more sensitive to considerations of medical ethics and medical utility, but is less sensitive to probabilities of actually successfully treating the patient or coming up with a definitive diagnosis. It more or less balances the utility of either testing or treatment at any given stage of the process.

A new approach is to work from first principles (the four cornerstones). Instead of narrowing down the diagnostic field by proposing a disease and seeing if it fits the symptoms, this approach focuses more on etiology - which dysfunction would lead to the symptoms being observed in the patient. Proponents of this approach believe it can be adapted to the use of artificial intelligence through the use of system theory - building a digital model of the function of the human body and letting the system work through dysfunctions until it determines the correct diagnosis.

Diagnostic opinionEdit

However, a diagnosis can take many forms. It might be a matter of naming the disease, lesion, dysfunction or disability. It might be a management-naming or prognosis-naming exercise. It may indicate either degree of abnormality on a continuum or kind of abnormality in a classification. It’s influenced by non-medical factors such as power, ethics and financial incentives for patient or doctor. It can be a brief summation or an extensive formulation, even taking the form of a story or metaphor. It might be a means of communication such as a computer code through which it triggers payment, prescription, notification, information or advice. It might be pathogenic or salutogenic. It’s generally uncertain and provisional.

Indication for diagnostic procedureEdit

The initial task is to detect a medical indication to perform a diagnostic procedure. Indications include:

  • Detection of any deviation from what is known to be normal, such as can be described in terms of, for example, anatomy, physiology, pathology, psychology and homeostasis (regarding mechanisms to keep body systems in balance). Knowledge of what is normal and measuring of the patient's current condition against those norms can assist in determining the patient's particular departure from homeostasis and the degree of departure, which in turn can assist in quantifying the indication for further diagnostic processing.
  • A complaint expressed by a patient.
  • The fact that a patient has sought a diagnostician can itself be an indication to perform a diagnostic procedure. For example, in a doctor's visit, the physician may already start performing a diagnostic procedure by watching the gait of the patient from the waiting room to the doctor's office even before she or he has started to present any complaints.

Even during an already ongoing diagnostic procedure, there can be an indication to perform another, separate, diagnostic procedure for another, potentially concomitant, disease or condition. This may occur as a result of an incidental finding of a sign unrelated to the parameter of interest, such as can occur in comprehensive tests such as radiological studies like magnetic resonance imaging or blood test panels that also include blood tests that are not relevant for the ongoing diagnosis.

In addition, it has been noted that running diagnostic tests often results in less certainty about the diagnosis. All diagnostic tests have limitations, particularly the possibility of a "false positive". As such, the physicians presented with a "positive" test must stop and think whether the positive really indicates the presence of the disease, or whether it is merely a mistake inherent in the testing methods (see, for example, Role Model, where an HIV-negative patient tests positive). This problem is compounded for rare conditions, where a false positive is far more likely than a real positive.

General componentsEdit

General components, which are present in a diagnostic procedure in most of the various available methods include:

  • Complementing the already given information with further data gathering, which may include questions of the medical history (potentially from other people close to the patient as well), physical examination and various diagnostic tests. A diagnostic test is any kind of medical test performed to aid in the diagnosis or detection of disease. Diagnostic tests can also be used to provide prognostic information on people with established disease.
  • Processing of the answers, findings or other results. Consultations with other providers and specialists in the field may be sought.

Specific methodsEdit

Assessment and treatment algorithm for overweight and obesity

A medical algorithm for assessing and treating obesity from the U.S. Department of Human Health, via Wikipedia

There are a number of methods or techniques that can be used in a diagnostic procedure, including performing a differential diagnosis or following medical algorithms.

Differential diagnosisEdit

Main article Differential diagnosis

The method of differential diagnosis is based on finding as many candidate diseases or conditions as possible that can possibly cause the signs or symptoms, followed by a process of elimination or at least of rendering the entries more or less probable by further medical tests and other processing until, aiming to reach the point where only one candidate disease or condition remains as probable. The final result may also remain a list of possible conditions, ranked in order of probability or severity.

The resultant diagnostic opinion by this method can be regarded more or less as a diagnosis of exclusion. Even if it doesn't result in a single probable disease or condition, it can at least rule out any imminently life-threatening conditions.

Unless the provider is certain of the condition present, further medical tests, such as medical imaging, are performed or scheduled in part to confirm or disprove the diagnosis but also to document the patient's status and keep the patient's medical history up to date.

If unexpected findings are made during this process, the initial hypothesis may be ruled out and the provider must then consider other hypotheses.

Pattern recognitionEdit

In a pattern recognition method the provider uses experience to recognize a pattern of clinical characteristics. It is mainly based on certain symptoms or signs being associated with certain diseases or conditions, not necessarily involving the more cognitive processing involved in a differential diagnosis.

This may be the primary method used in cases where diseases are "obvious", or the provider's experience may enable him or her to recognize the condition quickly. Theoretically, a certain pattern of signs or symptoms can be directly associated with a certain therapy, even without a definite decision regarding what is the actual disease, but such a compromise carries a substantial risk of missing a diagnosis which actually has a different therapy so it may be limited to cases where no diagnosis can be made.

Diagnostic criteriaEdit

The term diagnostic criteria designates the specific combination of signs, symptoms, and test results that the clinician uses to attempt to determine the correct diagnosis.

Some examples of diagnostic criteria, also known as clinical case definitions, are:

Clinical decision support systemEdit

Clinical decision support systems are interactive computer programs designed to assist health professionals with decision-making tasks. The clinician interacts with the software utilizing both the clinician’s knowledge and the software to make a better analysis of the patients data than either human or software could make on their own. Typically the system makes suggestions for the clinician to look through and the clinician picks useful information and removes erroneous suggestions.

Other diagnostic procedure methodsEdit

Other methods that can be used in performing a diagnostic procedure include:

  • Usage of medical algorithms
  • An "exhaustive method", in which every possible question is asked and all possible data is collected.
  • Use of a sensory pill camera that collects and transmits physiological information after being swallowed.
  • Using optical coherence tomography to produce detailed images of the brain or other soft tissue, through a "window" made of zirconia that has been modified to be transparent and implanted in the skull.

Diagnostic opinion and its effects Edit

Once a diagnostic opinion has been reached, the provider is able to propose a management plan, which will include treatment as well as plans for follow-up. From this point on, in addition to treating the patient's condition, the provider can educate the patient about the etiology, progression, prognosis, other outcomes, and possible treatments of her or his ailments, as well as providing advice for maintaining health.

A treatment plan is proposed which may include therapy and follow-up consultations and tests to monitor the condition and the progress of the treatment, if needed, usually according to the medical guidelines provided by the medical field on the treatment of the particular illness.

Relevant information should be added to the medical record of the patient.

A failure to respond to treatments that would normally work may indicate a need for review of the diagnosis.

Additional types of diagnosisEdit

Sub-types of diagnoses include:

Clinical diagnosis
A diagnosis made on the basis of medical signs and patient-reported symptoms, rather than diagnostic tests
Laboratory diagnosis
A diagnosis based significantly on laboratory reports or test results, rather than the physical examination of the patient. For instance, a proper diagnosis of infectious diseases usually requires both an examination of signs and symptoms, as well as laboratory characteristics of the pathogen involved.
Radiology diagnosis
A diagnosis based primarily on the results from medical imaging studies. Greenstick fractures are common radiological diagnoses.
Principal diagnosis
The single medical diagnosis that is most relevant to the patient's chief complaint or need for treatment. Many patients have additional diagnoses.
Admitting diagnosis
The diagnosis given as the reason why the patient was admitted to the hospital; it may differ from the actual problem or from the discharge diagnoses, which are the diagnoses recorded when the patient is discharged from the hospital.
Differential diagnosis
A process of identifying all of the possible diagnoses that could be connected to the signs, symptoms, and lab findings, and then ruling out diagnoses until a final determination can be made.
Diagnostic criteria
Designates the combination of signs, symptoms, and test results that the clinician uses to attempt to determine the correct diagnosis. They are standards, normally published by international committees, and they are designed to offer the best sensitivity and specificity possible, respect the presence of a condition, with the state-of-the-art technology.
Prenatal diagnosis
Diagnosis work done before birth. For an example, see Fetal Position.
Diagnosis of exclusion
A medical condition whose presence cannot be established with complete confidence from history, examination or testing. Diagnosis is therefore by elimination of all other reasonable possibilities.
Dual diagnosis
The diagnosis of two related, but separate, medical conditions or co-morbidities; the term almost always refers to a diagnosis of a serious mental illness and a substance addiction.
The diagnosis or identification of a medical conditions in oneself. Self-diagnosis is very common and typically accurate for everyday conditions, such as headaches, menstrual cramps, and head lice.
Remote diagnosis
A type of telemedicine that diagnoses a patient without being physically in the same room as the patient. For an example see Frozen
Nursing diagnosis
Rather than focusing on biological processes, a nursing diagnosis identifies people's responses to situations in their lives, such as a readiness to change or a willingness to accept assistance.
Computer-aided diagnosis
Providing symptoms allows the computer to identify the problem and diagnose the user to the best of its ability. Health screening begins by identifying the part of the body where the symptoms are located; the computer cross-references a database for the corresponding disease and presents a diagnosis. However, although computer diagnosis has been proposed since the late 1950s, at present, diagnosis seems to have eluded the capacity of current expert systems and appears to be poorly suited to symbolic logic and statistical analysis.
The diagnosis of "disease" that will never cause symptoms, distress, or death during a patient's lifetime. For example, in recent years, oncology has been criticized for its emphasis on "early detection" of cancers that have little chance of spreading, resulting in patients being treated where monitoring might be the more appropriate option.
Wastebasket diagnosis
A vague, or even completely fake, medical or psychiatric label given to the patient or to the medical records department for essentially non-medical reasons, such as to reassure the patient by providing an official-sounding label, to make the provider look effective, or to obtain approval for treatment. This term is also used as a derogatory label for disputed, poorly described, overused, or questionably classified diagnoses, such as pouchitis and senility, or to dismiss diagnoses that amount to overmedicalization, such as the labeling of normal responses to physical hunger as reactive hypoglycemia.
Retrospective diagnosis
The labeling of an illness in a historical figure or specific historical event using modern knowledge, methods and disease classifications. For example, Charles Darwin suffered from severe symptoms of chest pain and breathing difficulties for most of his adult life. He was never diagnosed and treatment was ineffective, although the problem disappeared as he aged. Originally modern physicians proposed that he had Chagas Disease from his trip to South America. However, more recently, physicians believe he was merely suffering from Anxiety attack.


Overdiagnosis is the diagnosis of "disease" that will never cause symptoms or death during a patient's lifetime. It is a problem because it turns people into patients unnecessarily and because it can lead to economic waste (overutilization) and treatments that may cause harm. Overdiagnosis occurs when a disease is diagnosed correctly, but the diagnosis is irrelevant. A correct diagnosis may be irrelevant because treatment for the disease is not available, not needed, or not wanted.


Most people will experience at least one diagnostic error in their lifetime, according to a 2015 report by the National Academies of Sciences, Engineering, and Medicine.

Causes and factors of error in diagnosis are:

  • the manifestation of disease are not sufficiently noticeable
  • a disease is omitted from consideration
  • too much significance is given to some aspect of the diagnosis
  • the condition is a rare disease with symptoms suggestive of many other conditions
  • the condition has a rare presentation

As shown several times on the series, incorrect diagnosis is a very common (if not the most common) cause for the commencement of a malpractice suit. In addition, as was discussed in Post Mortem, it is far easier to diagnose a patient after death or serious complications as during an autopsy, the physician can perform tests without considering the discomfort or safety of the patient.

Other difficulties Edit

Modern medicine has defined thousands of distinct conditions and even a specialist may deal with hundreds of different possibilities. In oncology, over 200 different distinct conditions have been identified and yet oncologists are also expected to be able to distinguish conditions that mimic cancer or dozens of complications that can arise in a patient with cancer, such as paraneoplastic syndromes. As such, diagnosis can be difficult, and doctors have to be trained how to do it appropriately. There are often several hurdles to determining an appropriate diagnosis:

  • Radically different diseases often manifest the same symptoms. For example, both a heart attack and severe heartburn can cause extreme chest pain.
  • Some diagnostic procedures are painful, expensive, invasive or dangerous to the patient. A good example is a biopsy, which is used to diagnose many serious conditions.
  • Some simple diseases are nevertheless so rare in some parts of the world that a doctor may not have been exposed to it before. For example, malaria is easily recognized by doctors in developing countries, but a doctor in a developed nation may never have seen a case and may confuse it with other conditions that cause jaundice.
  • As House often points out, patients will lie about relevant considerations, such as whether they have engaged in extramarital sex. This often robs doctors of the clues they require to make the appropriate diagnosis.

Lag timeEdit

When making a medical diagnosis, a lag time is a delay in time until a step towards diagnosis of a disease or condition is made. Types of lag times are mainly:

  • Onset-to-medical encounter lag time, the time from onset of symptoms until visiting a health care provider
  • Encounter-to-diagnosis lag time, the time from first medical encounter to diagnosis

Medical education Edit

Diagnosis is one of the most difficult skills to teach medical students. Ironically, this is often due to the student's diligence and fresh knowledge. The diligence results in the student collecting too much information instead of focusing on the most important clinical signs. Secondly, the fact that the student is exposed to a huge number of conditions often means that they do not distinguish between the "horses" and the "zebras", leading to the first rule of diagnosis - "When you hear hoofbeats....".

During their training, students have to be taught to start the inquiry by focusing on the most important clinical signs, working through the most common conditions, and quickly ruling out conditions that might be dangerous (such as a heart attack for chest pain).

In practice Edit

In the United States, Canada and Great Britain, there are generally two "front lines" of medical diagnosis - the family physician (or general practitioner) and the emergency room doctor. In both cases, physicians are expected to make common diagnoses and to prescribe the appropriate treatment.

Where the front line doctor finds that no definitive diagnosis can be reached, the next step is to refer the patient to a specialist. This decision is usually based on the primary complaint of the patient or the results of preliminary tests. However, as House himself has pointed out, this often leads to "choose your specialist, choose your diagnosis" as specialists usually focus on possibilities within their field and ignore possibilities outside of it.

In a hospital setting, a specialist may request a consult from a sub-specialist or from a specialist in another field. In a clinical setting, it is more common for the specialist to refer the matter back to the family physician for follow up with the patient.

Unlike in the series, it is almost unheard of for a patient with an undiagnosed condition to be treated continuously for several days to a week by a single attending physician in order to reach a definitive diagnosis. When a patient does have a rare condition, it is far more likely that the patient will be moved around several physicians, often in several different hospitals, over a period of weeks or even months before the correct diagnosis is reached. This is largely due to the time demands on physicians and billing systems that emphasize seeing as many patients as possible in as short a time as possible. In addition, unless a test is very urgent, samples are generally sent out to outside labs which may take several days to provide the results back to the physician. At that point, the physician may have dozens of results to review before they can get back to the patient.

On the series Edit

Gregory House clearly prefers the technique of the differential diagnosis as part of his method. He wants his fellows to suggest as many possible diagnoses as possible in a short period of time as he sits back and rules out possibilities based on known information. He encourages them to consider rare diagnoses first as opposed to the "proper" practice of considering the mundane first. Despite him often calling other physicians "idiots", he still trusts their judgment to rule out obvious diagnoses before coming to him.

In addition to relying on medical tests and diagnostic trials, House is also a proponent of gathering as much information as possible without using these methods. He insists on a proper medical history and will often re-perform a medical history if he does not believe the admitting physicians have done an appropriately thorough job. That being said, he also believes greatly in the maxim everybody lies and will often question his fellows and the patient when information in the medical history seems incomplete or contradictory. He also utilizes the environmental scan to a great extent despite its questionable medical ethics and invasion of patient privacy.

After an initial diagnosis, House will often start treatment immediately before waiting for the results of tests. He will often order treatment even when he has only narrowed down the possible diagnoses to two or three rather than a single definitive diagnosis. In such cases, the working diagnosis is usually the one that may have the most serious short term consequences even though treatment for that condition may be dangerous if the patient has the other condition. He commonly orders a diagnostic trial - treating the patient to determine what the consequences will be. When he is particularly frustrated, he will often throw every treatment he can think of at a patient even with no working diagnosis.

However, House is never wedded to any particular diagnosis and when treatment does not have the desired effect, he will often throw out all his previous assumptions and start the process all over again. He is also not above re-visiting diagnoses he has previously rejected.

Above all, House believes that objectivity about the diagnosis is crucial. Although this brings an egalitarian approach to his method, it also distances him from his patients, whom he prefers to never meet lest his objectivity be compromised.

Medical diagnosis at Wikipedia - This article uses text from Wikipedia under the Creative Commons license

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