Standardization of a filter-paper technique for blood sampling.

Blood sampling on filter paper has many potential advantages compared to sampling by venepuncture. However, the method is poorly standardized, and some variables affecting its usefulness were therefore explored; different filter papers were compared and an optimal elution procedure was determined. The quantity of eluted IgG, IgM and IgA was determined by single radial diffusion, and antibody activity was determined in an enzyme immunoassay. Comparison to serum titres was facilitated by calculation of the dilution factor. Filter papers containing drops of whole blood from a Swedish patient with Schistosoma mansoni infection were stored at different temperatures over different periods of time. Antibodies of different classes could be extracted and antibody activity demonstrated after up to 30 weeks of storage. The reproducibility of the technique was good, and comparison to serum titres can easily be calculated.