Measurement of ceruloplasmin from its oxidase activity in serum by use of o-dianisidine dihydrochloride.

We have developed a new method for determination of serum ceruloplasmin from its oxidase activity, in which o-dianisidine dihydrochioride is used as substrate. o-Dianisidine dihydrochloride is more stable than is the more widely used p-phenylenediamine substrate, and forms a stable product that is measured at 540 nm. Correlation was good between results of this method and those obtained with both a p-phenylenediamine substrate method (r 0.98) and a radial immunodiff usion procedure (r 0.97). There is little or no interference from reducing or colored components of serum. The coefficient of variation (day-to-day) for the method was 4.2%. A normal range of 62-140 U/liter has been determinedby the reported method.