The impact of comorbidity on outcomes.

Patients often have other diseases, illnesses, or conditions in addition to the disease under study. These other medical conditions are referred to as comorbidity. Comorbidity can impact on diagnosis, prognosis, and selection of therapy. There are a variety of instruments available to measure the type and severity of comorbid ailments. Comorbidity information can be obtained from direct discussions with the patient, a review of the medical record, or from electronic databases that contain billing information. The method of comorbidity assessment can impact on the interpretation of results. Accurate comorbid information will improve the conduct of and generalizability of clinical trials, evaluation of outcomes from observational research, population-based epidemiological studies, and patient-physician communication.