Complement factor D concentrations in normal sera: comparison of immunochemical and functional determinations.

The concentration of factor D (D) was determined in the sera of 144 healthy adults and 29 healthy children by enzyme amplified electroimmunoassay (EAE), and by a hemolysis in gel (HIG) assay for D. The 95% geometric confidence areas for D in adults were 75-143% as determined by EAE, and 65-171% by the functional assay. The concentrations were given in per cent of a reference serum pool containing 1.6 mg/l of D as measured by EAE. The correlation coefficient between D values obtained by the two methods was r = 0.52 (p less than 0.001). D levels were lower in children than in adults. In the EAE purified D, and pathological sera with very high D Concentrations, gave lower precipitation peaks with dilutions performed in buffer than with dilutions in D depleted serum or human serum albumin.