Some studies on the polyethylene glycol turbidity method for detecting immune complexes in serum

A rapid and simple method for detecting circulating immune complexes based on turbidity measurements following polyethylene glycol precipitation was studied with regard to its suitability as a routine assay in clinical laboratories. This method was found to have an acceptable degree of precision provided the temperature was carefully controlled. The mean value obtained with a group for 70 blood donors was 0.09 (SD 0.05) and the 90th percentile value was 0.16. There was no significant difference between values obtained from groups divided on the basis of age or sex. Of 70 diabetic sera assayed by the polyethylene glycol turbidity method, 20% gave positive values although only 10% were strongly positive. The corresponding figures for the solid phase Clq binding method were 15.7% and 14.3%, respectively. Correlation between the two methods was poor. It was concluded that although both methods have a similar likelihood of detecting immune complexes in randomly selected diabetics, it is probable that different immune complexes were being detected.