How to understand medical decisions

What does each diagnosis mean, how probable is it, how severe is it, what is its time course and where could I read about it?

A diagnosis (e.g. diabetes mellitus) is the title to what a doctor thinks is wrong with a patient.  By asking what the diagnosis means, you are asking for a description of what processes the title represents.  The processes represented by a diagnostic term will be made up of some observable features that have been confirmed to be present already (e.g. the patient’s reported fatigue and a single high blood sugar) together with hidden features that are only being predicted or imagined (e.g. the features that confirm diabetes), and its causes and complications (e.g. future diabetic eye disease).  A diagnosis therefore consists of a large number of 'pictured' predictions, each with its own degree of certainty or probability.


Hidden features

Some of the hitherto hidden features could be confirmed to exist (or not to exist) later (e.g. improvement of a symptom with treatment) but some will always be imagined (e.g. the molecules and atoms of defective proteins).  Many of the features that may be confirmed later are causes and complications, which if present, become diagnoses in their own right (e.g. diabetic eye disease).  They can then be added to the list of diagnoses with their own subheadings of supportive findings and plans.  The most important prediction from the patient’s point of view is the response to treatment of different kinds.


Severity and uncertainty

The severity of a diagnosis is important as this can affect treatment and the probability of complications.  In some mild cases treatment may not make a difference and so the treatment would not be helpful.  In severe cases some treatments may again not be effective because it may be too late to make a difference.  The change in severity with time is also important as this can be used to assess the effectiveness of treatment.  If the diagnosis is uncertain, then a number of patients treated for the diagnosis would not have the condition at all so that too few patients might benefit to make giving the treatment worthwhile.  In other cases it may be dangerous to delay starting treatment but not dangerous to give it unnecessarily, so it might be started ‘just in case’.



There are many books and websites available where the reader will be given descriptions of what diagnostic and other terms mean.  One of the most reliable and helpful is NHS Choices - Health A to Z (click here to access the NHS Health A to Z website).  



If the reader is worried that a diagnosis might apply to them, reading about it without having spoken to a doctor will increase that worry. The reason for this is that the reader will not be considering other diagnoses that could also account for the symptoms.  Reading that many of the reader's symptoms can be caused by the diagnosis may falsely increase a sense of certainty in that diagnosis.  A doctor should think of other possibilities as well e.g. by considering the causes of good diagnostic leads.



© Huw Llewelyn 2016