Diagnosis

# Overview
In general, diagnosis (plural diagnoses) has two distinct dictionary definitions. The first definition is "the recognition of a disease or condition by its outward signs and symptoms", while the second definition is "the analysis of the underlying physiological/biochemical cause(s) of a disease or condition".
Diagnosis covers a broad spectrum, or spectra, of testing in some form of analysis; collective reasoning using such tests is called the method of diagnostics, leading then to the results of those tests by ideal (ethics) would then be considered a diagnosis, but not necessarily the correct one.
In medicine, diagnosis or diagnostics is the process of identifying a medical condition or disease by its signs, symptoms, and from the results of various diagnostic procedures. The conclusion reached through this process is called a diagnosis. The term "diagnostic criteria" designates the combination of symptoms which allows the doctor to ascertain the diagnosis of the respective disease.
Typically, someone with abnormal symptoms will consult a physician, who will then obtain a history of the patient's illness and examine him for signs of disease. The physician will formulate a hypothesis of likely diagnoses and in many cases will obtain further testing to confirm or clarify the diagnosis before providing treatment.
Medical tests commonly performed are measuring blood pressure, checking the pulse rate, listening to the heart with a stethoscope, urine tests, fecal tests, saliva tests, blood tests, medical imaging, electrocardiogram, hydrogen breath test and occasionally biopsy.
The word diagnosis is derived from the Greek words dia which means "by", and gnosis which means "knowledge". The verb is diagnose and a person diagnosing could be considered a diagnostician.

# Relationship of diagnosis to medical practice
A physician's job is to know the human body and its functions in terms of normality (homeostasis). The four cornerstones of diagnostic medicine, each essential for understanding homeostasis, are: anatomy (the structure of the human body), physiology (how the body works), pathology (what can go wrong with the anatomy and physiology) and psychology (thought and behavior). Once the doctor knows what is normal and can measure the patient's current condition against those norms, she or he can then determine the patient's particular departure from homeostasis and the degree of departure. This is called the diagnosis. Once a diagnosis has been reached, the doctor 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 doctor educates the patient about the causes, progression, outcomes, and possible treatments of his ailments, as well as providing advice for maintaining health.
It should be noted however, that medical diagnosis in psychology or psychiatry is problematic. Apart from the fact that there are differing theoretical views toward mental conditions and that there are few "lab" tests available for various major disorders (e.g., clinical depression), a causal analysis with respect to symptomatology and disorder/disease is not always possible. As a result, most if not all mental conditions, function as both symptoms as well as disorders. There are often functional descriptions provided for psychological disorders and these are vulnerable to circular reasoning due to the etiological fuzziness inherent of these diagnostic categories. (BDG, 2006)

# Diagnostic procedure
Diagnosis is a fluid process in which the physician responds to information garnered from the patient and others, from a physical examination of the patient, and from medical tests performed upon the patient.
The doctor should consider the patient in his 'well' context rather than simply as a walking medical condition. This entails assessing the socio-political context of the patient (family, work, stress, beliefs), in addition to the patient's physical body, as this often offers vital clues to the patient's condition and its management.
The process of diagnosis begins when the patient consults the doctor and presents a set of complaints (the symptoms). If the patient is unconscious, this condition is the de facto complaint. The doctor then obtains further information from the patient himself (and from those who know him, if present) about the patient's symptoms, his previous state of health, living conditions, and so forth.
Rather than consider the myriad diseases that could afflict the patient, the physician narrows down the possibilities to the illnesses likely to account for the apparent symptoms, making a list of only those conditions that could account for what is wrong with the patient. These are generally ranked in order of probability.
The doctor then conducts a physical examination of the patient, studies the patient's medical record, and asks further questions as he goes, in an effort to rule out as many of the potential conditions as possible. When the list is narrowed down to a single condition, this is called the differential diagnosis, and provides the basis for a hypothesis of what is ailing the patient.
Unless the physician is certain of the condition present, further medical tests are performed or scheduled (such as medical imaging), in part to confirm or disprove the diagnosis but also to document the patient's status to keep the patient's medical history up to date. Consultations with other physicians and specialists in the field may be sought. If unexpected findings are made during this process, the initial hypothesis may be ruled out and the physician must then consider other hypotheses.
Despite all of these complexities, most patient consultations are relatively brief, because many diseases are obvious, or the physician's experience may enable him to recognize the condition quickly. Another factor is that the decision trees used for most diagnostic hypothesis testing are relatively short.
Once the physician has completed the diagnosis, he explains the prognosis to the patient and proposes a treatment plan which includes therapy and follow-up (further consultations and tests to monitor the condition and the progress of the treatment, if needed), usually according to the guideline provided by the medical field on the treatment of the particular illness.
Treatment itself may indicate a need for review of the diagnosis if there is a failure to respond to treatments that would normally work.

# History of medical diagnostics
The history of medical diagnosis began in earnest from the enlightened days of Hippocrates in ancient Greece but is far from perfect despite the enormous bounty of information made available by medical research including the sequencing of the human genome. The practice of diagnosis continues to be dominated by theories set down in the early 1900s.

## Ancient Greece
Over two thousand years ago, Hippocrates recorded the association between disease and heredity. In similar fashion, Pythagoras noted the association between metabolism and heredity (allergy to Fava beans). The medical community, however, has only recently acknowledged the importance of genetics and its relevance to mainstream medicine.

## The Oslerian ideal
The ideals of William Osler who transformed the practice of medicine in the early 1900s were based on the principles of the diagnosis and treatment of disease. According to Osler, the functions of a physician were to be able to identify disease and its manifestations, understand its mechanisms, how it may be prevented and how it may be cured. For his medical students he believed that the best textbook was the patient himself  analysis of morbid anatomy and pathology were the keys. The Oslerian ideal continues today, as the basis of the Doctors strategy is, "What disease does this patient have and what is the best way for treatment?" The emphasis is on the classification of the disease in order to use the remedies available for its effects to be reversed or ameliorated. The human being in question is representative of a class of people with this type of disease whereas the biological individuality of this person is not given any great weight.

## Garrod's view
The successor to William Osler as Regius Professor at Oxford was Archibald Garrod. Garrod echoed the observations of his Greek counterparts of two millennia ago, ...our chemical individualities are due to our chemical merits as well as our chemical shortcomings; and it is more nearly true to say that the factors which confer upon us our predispositions to and immunities from various mishaps which are spoken of as diseases, are inherent in our very chemical structure; and even in the molecular groupings which confer upon us our individualities, and which went into the making of the chromosomes from which we sprang. Considering that the time that he formulated these ideas were the early 1900's, and the knowledge of DNA encoding genes that in turn encoded proteins responsible for bodily structure and functions not being discovered until some fifty years later it took some time before medicine could fully appreciate the fundamental importance of his concept of diagnosis.

## Present-day Oslerian practice
Whereas Osler laid the founding principles by which medicine should be practiced, Garrod placed these principles in a greater context of a chemical individuality that is inherited and is subject to the mechanisms of evolutionary selection. The Oslerian ideal of medical practice continues to dominate medical philosophy today. The patient is a collective of symptoms to be characterized and analyzed algorithmically in order to draw a diagnosis and subsequently produce a strategy of treatment. Medicine is about problems based solutions. In keeping with this philosophy, today's pathology reports provide a momentary snapshot of the patient's biochemical profile, highlighting the end result of the disease process.

## Influence of DNA technology
Garrod's conception of biological individuality was confirmed with the advent of the sequencing of the human genome. Finally the subtle relationship between inheritance, individuality and environment became apparent via the variations detected in DNA. In each patient's DNA lies a script for how their bodies will change and become ill as well as how they will handle the assaults of the environment from the beginning of their life to its end. It is hoped that by knowing a patient's genes that the biological strengths and weaknesses in respect to these assaults will be revealed and disease processes can be predicted before they have the opportunity to manifest. Although knowledge in this area is far from complete, there are already medical interventions based on this. More importantly, the physician, forewarned with this knowledge can guide the patient towards appropriate lifestyle changes to anticipate and mitigate disease processes.