Diseases may be classified by etiology (cause), pathogenesis (mechanism in which a professional induces disease) or even by symptom. As an alternative, diseases may be classified based on data from a organ system they involve, however this is typically complicated when several diseases affect multiple organs.

One of a independent problems using diagnostics is that diseases typically just can non exist as defined & classified clearly especially whilst pathogenesis or even causality is not known. And so, symptomatic terms typically come in point of fact single consequences or even sets of illness (syndromes).