Diagnosis

Diagnosis (from the Greek words dia = by and gnosis = knowledge) is the process of identifying a disease by its signs, symptoms and results of various diagnostic procedures. The conclusion reached through that process is also called a diagnosis.

Hypothesis testing

History taking is a fluid process that adapts to the information as it is presented. Almost invariably the patient presents with a complaint. Even the unconscious patient presents with the implicit complaint of being unconscious. This presenting complaint leads to the formation of hypotheses. Rather than consider the myriad of diseases that could afflict the patient, the physician narrows down the possibilities to those conditions likely to account for the presenting complaint. The history taking then proceeds to test these hypotheses, often narrowing down the diagnosis within a few questions. Sometimes the initial hypotheses are ruled out and the physician must then move on to look at other hypotheses or multiple ones. Occam's razor is then invoked to attempt to simplify the number of provisional diagnoses and it is only with some reluctance that a physician will make several provisional diagnoses to explain the symptoms elicited.

Related Topics:
Hypotheses - Occam's razor

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The physician then moves on to the physical examination. However, the hypothesis testing does not end at this point. Signs may confirm the provisional diagnosis or cause the physician to consider the question further and even lead to more questioning. An unexpected finding on examination may cause the physician to reconsider the initial diagnosis.

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At this point the physician usually has at least a differential diagnosis and probably a provisional diagnosis if not a firm diagnosis. Further tests are then requested, in part to confirm or disprove the diagnosis but also to document the status at that time and before treatment is started. Consultations with other physicians and specialists in the field may be sought.

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Treatment itself may indicate a need for review of the diagnosis if there is a failure to respond to treatments that would normally work.

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Despite all of these complexities, most consultations are relatively brief, partly because many diseases are common and pattern recognition allows the physician to recognize the diagnosis early, but also because the decision trees of most hypothesis testing are relatively short.

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