Many patients decide to visit a doctor when the same symptom occurs for several days, and the situation does not change or even gets worse. In this case, a new patient informs about a fever for three days and asks for help. To come to one correct diagnosis, it is necessary to identify several differential diagnoses and use gained knowledge and probability experiences.
Cahan underlines that there is usually no escape from probabilities in making diagnoses because any physician has to compare the patient’s situation to a set of criteria for possible diseases. Certain medical knowledge, clinical experiences, and personal characteristics of patients, as well as their past medical history, can play an important role and cannot be ignored.
The update of probability is possible when the known conditions are used in accordance with the formula called a conditional probability. Cahan suggests relating a symptom that may be given to a disease with a disease that may give a presentation. Such factors as age, the presence/absence of other symptoms, past surgeries, and allergies have to be considered. New study results should not be ignored because researchers can identify additional sources of allergies, and fever being one of the outcomes.
The source and causes of probabilities to change include the fact that medicine, pharmacology, and health care are constantly improved and developed. The impact of genetics should be mentioned because the evaluation of genes helps discover new reasons and explanations of some diseases when treatment plans and surgeries cannot help. Probability and new sources are inevitable in diagnosis-making, and physicians cannot neglect or break the laws of probability.