Table 1.

Impact of Comorbidity on Clinical Care: Overview of Classification Systems

Author	Classification	Definition
Kaplan et al12,34,35	Diagnostic comorbidity	“An associated disease [whose]…manifestations can simulate those of the index disease” (eg, pneumonia and pulmonary infarction)
	Prognostic comorbidity	Diseases “[in relation to an index disease] graded according to their anticipated effects on therapy and life expectancy [as]”
	Cogent	“Comorbid ailments expected to impair a patient’s long-term survival” (eg, recent severe stroke)
	Noncogent	“Other ailments” (eg, congestive heart failure or myocardial infarction more than 6 months old)
Angold et al16	Homotypic comorbidity	“Disorders within a diagnostic grouping” (eg, major depression and dysthymia)
	Heteroptypic comorbidity	“Disorders from different diagnostic groupings” (eg, major depression and conduct disorder)”
Piette and Kerr36	Concordant comorbidity	“[Diseases as] parts of the same pathophysiologic risk profile and more likely to share the same management and are more likely to be the focus of the same disease management plan” (eg, type 2 diabetes mellitus and hypertension)
	Discordant comorbidity	Diseases that are “not directly related in either pathogenesis or management and do not share an underlying predisposing factor” (eg, type 2 diabetes mellitus and irritable bowel syndrome)