Determination of tetanus and diphtheria antitoxin content in dried samples of capillary blood: a convenient method applied to infants.

To assess the effect of vaccination of infants against tetanus and diphtheria capillary blood was drawn from 51 randomly selected healthy infants 2 years of age. The blood was applied directly to filter paper. In the laboratory the blood dots were eluted in phosphate buffered saline for 2 h at room temperature yielding 100% recovery of antitoxin activity. Serum volume in the blood dots was determined by calculation of dot area or by measuring albumin content in the eluted samples by means of rocket immunoelectrophoresis. These approaches were found to be equally applicable. Concentration of antitoxin to tetanus and diphtheria was assessed with ELISA and in vitro toxin neutralization assay respectively. Mean diphtheria antitoxin concentration was 0.53 IU/ml, and mean tetanus antitoxin concentration 4.1 IU/ml. Low initial immune response to diphtheria vaccination may be responsible for the risk among school children to have antitoxin concentration below protective level (reported elsewhere). In environments where diphtheria is disappearing a lowered vaccination response may be expected.