Clinical comorbidity was specific to disease pathology, psychologic distress, and somatic symptom amplification

To test the hypothesis that disease pathology, psychologic distress, and somatic symptom amplification separately influence health care use by investigating the patterns of comorbidity in patients with diabetes, anxiety, and upper respiratory tract infection (URTI), respectively.

Adult diabetes (n=4,365), anxiety (13,421), and URTI (9,854) cases, and 15,000 randomly selected controls were identified from a 1-year national survey of general practice consultations. Comorbidity was based on a standard clinical morbidity classification used by general practitioners in actual consultations.

In case-control analyses of 122 morbidities, the number of significant comorbid associations (P<.01) for diabetes was 30, anxiety was 72, and URTI was 49. These associations showed significant heterogeneity in the odds ratios estimated using Cochran's Q and I2 statistic, both between case groups and within each case group. Diabetes associations were stronger with peripheral vascular disease (odds ratio 2.7), candidiasis (2.5), cataract (2.4), obesity (2.2), and hypertension (1.7); anxiety with depressive disorder (4.1), affective psychosis (4.0), adjustment reaction (3.2), functional gastrointestinal disorders (2.5) and general symptoms (2.5); and URTI with nonspecific blood findings (5.5), bronchitis (5.2), and injury (3.5).

Our study shows patterns of clinical comorbidity specific to the case conditions that supports the hypothesis that different mechanisms (disease pathology, psychologic distress, and somatic symptom amplification) operate to influence consultation behavior and comorbidity.