In medicine, comorbidity (literally "additional morbidity") is either * The presence of one or more disorders (or diseases) in addition to a primary disease or disorder; or * The effect of such additional disorders or diseases.
In medicine, comorbidity describes the effect of all other diseases an individual patient might have other than the primary disease of interest. The Charlson Comorbidity is the most widely accepted, validated method, currently used to quantify such comorbidity.
Many tests attempt to standardize the “weight” or value of comorbid conditions, whether they are secondary or tertiary illnesses. Each test attempts to consolidate each individual comorbid condition into a single, predictive variable that measures mortality or other outcomes. Researchers have "validated" such tests because of their predictive value, but no one test is as yet recognized as a standard.
The term "comorbid" currently has two definitions: 1) to indicate a medical condition existing simultaneously but independently with another condition in a patient (this is the older and more "correct" definition) 2) to indicate a medical condition in a patient that causes, is caused by, or is otherwise related to another condition in the same patient (this is a newer, nonstandard definition and less well-accepted).
Since patients often don't know how severe their conditions are, originally to calculate the index nurses were supposed to go through the patient's chart and determine whether the patient had a particular condition. Subsequent studies have adapted it to a questionnaire for patients.
The original citation follows: Charlson ME, Pompei P, Ales KL, McKenzie CR (1987). A new method of classifying prognostic comorbidity in longitudinal studies: development and validation. J Chron Dis, 40(5): 373-383.
Patients who are more seriously ill tend to require more hospital resources than patients who are less seriously ill, even though they are admitted to the hospital for the same reason. Recognizing this, the diagnosis-related group (DRG) manual splits certain DRGs based on the presence of secondary diagnoses for specific complications or comorbidities (CC).
In psychiatry, psychology and mental health counseling comorbidity refers to the presence of more than one diagnosis occurring in an individual at the same time. In psychiatry, comorbidity does not necessarily imply the presence of multiple diseases, but instead can reflect our current inability to supply a single diagnosis that accounts for all symptoms. On the DSM Axis I, Major Depressive Disorder is a very common comorbid disorder. The Axis II personality disorders are often criticized because their comorbidity rates are excessively high, approaching 60% in some cases, indicating to critics the possibility that these categories of mental illness are too imprecisely distinguished to be usefully valid for diagnostic purposes and, thus, for deciding how treatment resources should be allocated.