Comorbidity

In medicine, a 'comorbidity exists when one or more relevant disorders coexist with the disease of primary interest. While comorbidities complicate diagnosis and treatment, they also have predictive value, and guide both the avoidance and preference of particular therapies.

Function and survival
Comorbidity may affect the ability of affected individuals to function and also their survival

Prognostic value
it may be used as a prognostic indicator for length of hospital stay, cost factors, and outcome or survival.

Drug selection
A comorbidity variously may make a particular treatment inadvisable, or recommend a different one. For hypertension, there are perhaps four basic drug classes that can be used for initial therapy. If the patient has comorbid asthma, beta-adrenergic antagonists would be contraindicated. If that same hypertensive patient had diabetes, an ACE inhibitor both treats hypertension and protects against renal damage of diabetes.