What Is Diagnostics
Diagnostics is a 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 signs, symptoms, and test results that allows the doctor to ascertain the diagnosis of the respective disease.
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.
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.