The term diagnostic criteria designates the combination of signs, symptoms, and test results that the clinician uses to attempt to determine the correct diagnosis. The plural of diagnosis is diagnoses, the verb is to diagnose, and a person who diagnoses is called a diagnostician. The word diagnosis (/daɪ.əɡˈnoʊsɨs/) is derived through Latin from the Greek word διάγιγνῶσκειν, meaning to discern or distinguish. This Greek word is formed from διά, meaning apart, and γιγνῶσκειν, meaning to learn.
Typically, a person with abnormal symptoms will consult a health care provider such as a physician, podiatrist, nurse practitioner, physical therapist or physicians assistant, who will then obtain a medical history of the patient's illness and perform a physical examination for signs of disease. The provider 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.
For instance, a common disorder such as pneumonia was nevertheless used as a diagnosis before the germ theory was accepted, and the disease was defined as a complex of many symptoms consisting of cough, sputum production, fever and chills. Later, as the actual cause was assigned to micro-organisms, the term diagnosis included the causality, e.g., pneumococcal pneumonia, suggesting not only a spectrum of symptoms but also a cause for the symptoms.
Advances in medicine could be described as a shift from definition #1 to definition #2 as scientific causalities were discovered. This differentiation of the term diagnosis is critically important because widespread disagreement exists between medical and psychiatric practitioners as to whether causalities for various diseases and disorders are known or not. If causalities are assumed to be known, then authentic cures can be obtained by correcting the causal abnormalities. If causalities are assumed to be unknown, then palliative treatments to reduce symptoms are the best treatments possible.
Diagnosis in medical practice
A provider'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 provider 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 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 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)
The diagnostic process is fluid in which the provider gathers information from the patient and others, from a physical examination of the patient, and from medical tests performed upon the patient.
There are a number of techniques used by providers to obtain a correct diagnosis:
- exhaustive method
- every possible question is asked and all possible data is collected.
- algorithmic method
- the provider follows the steps of a proven strategy.
- pattern-recognition method
- the provider uses experience to recognise a pattern of clinical characteristics.
- differential diagnosis
- the provider uses the hypothetico-deductive method, a systematic, problem-focused method of inquiry.
The advanced clinician uses a combination of the pattern-recognition and hypothetico-deductive approaches.
The presence of some medical conditions cannot be established with complete confidence from examination or testing. Diagnosis is therefore by elimination of other reasonable possibilities, referred to as the diagnosis of exclusion.
The provider should consider the patient in their '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 provider and presents a set of complaints (symptoms). If the patient is unconscious, this condition is the de facto complaint. The provider then obtains further information from the patient and from those who know him or her, if present, about the patient's symptoms, their previous state of health, living conditions, and so forth.
Rather than consider the myriad diseases that could afflict the patient, the provider narrows down the possibilities to their illnesses likely to account for the apparent symptoms, making a list of only those disease (conditions) that could account for what is wrong with the patient. These are generally ranked in order of probability.
The provider then conducts a physical examination of the patient, studies the patient's medical record, and asks further questions 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 provider 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 providers 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 provider must then consider other hypotheses.
Despite all of these complexities, most patient consultations are relatively brief, because many diseases are obvious, or the providers experience may enable him or her to recognize the condition quickly. Another factor is that the decision tree is used for most diagnostic hypothesis testing are relatively short.
Once the provider has completed the diagnosis, the prognosis is explained to the patient and a treatment plan is proposed which includes therapy and follow-up consultations and tests to monitor the condition and the progress of the treatment, if needed, usually according to the medical 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.
A laboratory diagnosis is either a substitution or complement to the diagnosis made by examination of the patient. For instance, a proper diagnosis of infectious diseases usually requires both an examination of symptoms, as well as laboratory characteristics of the pathogen involved.
A diagnostic test is any kind of medical test performed to aid in the diagnosis or detection of disease. The possible benefits of a diagnostic test must be weighed against the costs of unnecessary tests and resulting unnecessary follow-up and possibly even unnecessary treatment of incidental findings.
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 leads to treatments that can only 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.
Errors in diagnosis
Causes 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
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.
The history of medical diagnosis began in earnest from the days of Imhotep in ancient Egypt and Hippocrates in ancient Greece. In Traditional Chinese Medicine, there are four diagnostic methods: inspection, auscultation-olfaction, interrogation, and palpation. A Babylonian medical textbook, the Diagnostic Handbook written by Esagil-kin-apli (fl. 1069-1046 BC), introduced the use of empiricism, logic and rationality in the diagnosis of an illness or disease. The book made use of logical rules in combining observed symptoms on the body of a patient with its diagnosis and prognosis. Esagil-kin-apli described the symptoms for many varieties of epilepsy and related ailments along with their diagnosis and prognosis.
The practice of diagnosis continues to be dominated by theories set down in the early 20th century.
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