Measurement of diphtheria and tetanus antitoxin in blood samples collected on filter paper disks.

Large-scale surveys of immunity to vaccine-preventable diseases may be limited by the inconvenience and expense involved in collection of blood by venepuncture. An alternative method of collecting blood on filter paper for measurement of immunity to diphtheria and tetanus is described. The precut filter disks (Elisadiscs), originally developed for serological diagnosis of disease in pigs, have advantages over previously described methods in that they allow safe handling of minimal volumes of blood (5 microliters) which can be conveniently quantified. To compare values obtained by venepuncture and fingerprick, paired samples were collected from 60 subjects and diphtheria and tetanus antitoxin concentrations were measured by ELISA. There was no significant difference detected between samples collected by the two methods. The results suggest that Elisadiscs are a reliable alternative to venepuncture for monitoring immunity to diphtheria and tetanus and would be useful for sample collection in remote areas and from children.