Determination of C3 phenotype in dried bloodstains using isoelectric focusing.

Fresh whole blood and bloodstains were analyzed by isoelectric focusing (IEF) to determine the C3 phenotype of the blood donor. Three common phenotypes exist as a result of two autosomal alleles. The three phenotypes can be identified in fresh serum or in serum samples which had been stored at -20 degrees C for more than a year. Bloodstains maintained in a desiccator at 25 or at 37 degrees C retained the native form of C3 which could be detected for at least two weeks. Beyond two weeks of storage, stains became difficult to phenotype due to decreased banding intensity. Bloodstains aged longer than one month could not be phenotyped. C3 could not be detected in human semen by the serological methods employed.