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In medicine,psychiatry and psychology comorbidity refers to:

  • The presence of one or more disorders (or diseases) in addition to a primary disease or disorder.
  • The interactive effect of such additional disorders or diseases.

Articles on the comorbidity of different conditions considered on the Psychology Wiki can be found at Category:Comorbidity of mental disorders

Charlson index

The Charlson co-morbidity index predicts the 1 year mortality for a patient who may have a range of co-morbid conditions such as heart disease, AIDS, or cancer (a total of 22 conditions). Each condition is assigned with a score of 1,2,3 or 6 depending on the risk of dying associated with this condition. Then the scores are summed up and given a total score which predicts mortality. For a physician, it's helpful in knowing how aggressively to treat a condition. e.g. A patient may have cancer, but also heart disease and diabetes so severe that the costs and risks of the treatment outweigh the short term benefit from treatment of the cancer.

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.

Comorbidity in psychology and psychiatry

In psychiatry, comorbidity refers to the presence of more than one mental disorder occurring in an individual at the same time. 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. Comorbidity is also found to be high in drug addicts, both physiologically and psychologically.

Comorbidity in physical health psychology

Comorbidity in medicine

In medicine, comorbidity describes the effect of all other diseases an individual patient might have other than the primary disease of interest. There is currently no accepted way 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.

Diagnosis-related group

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 DRGmanual splits certain DRGs based on the presence of secondary diagnoses for specific complications or comorbidities (CC).

See also

References & Bibliography

Key texts



  • 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.

Additional material



External links

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