Circulating immune complexes in unselected patients admitted to the medical service of a general hospital.

The platelet aggregation test was used to detect circulating immune complexes (CIC) in 567 patients admitted to a general hospital. One hundred and fourteen or 20.1% had positive tests compared to seven or 5.4% of 129 normal controls. When the hospitalized population was analyzed by disease group, significantly elevated CIC levels were found in 27 disease categories, including several common conditions not generally considered to be immunologically mediated, such as angina pectoris, myocardial infarction, congestive heart failure, pneumonia, pulmonary emboli, diabetes mellitus, infarction of the bowel, and carcinoma of the lung. These results indicated that an important problem in the interpretation of CIC levels in a particular condition may be the presence of complexes caused by common diseases coexisting with the condition being studied.