Investigations concerning the possibility to replace the Schick test by the passive hemagglutination reaction for evaluating the diphtheria immunity level in population.

The evaluation of Schick test results as compared to the results obtained by determination of diphtheria antitoxin concentration in blood using the neutralizing test on rabbit--Jensen on the one hand and to those obtained by the passive hemagglutination reaction on the other has revealed some discrepancies against the two tests: 7.09% (4.08% pseudo-protected, 3.01 pseudo-susceptible) as against TN-Jensen and 8.6% (5.59% pseudo-protected and 3.01% pseudo-susceptible) as against the passive hemagglutination reaction results. The reported discrepancies were due to the fact that the results of Schick test did not correlate perfectly with the amount of circulating antitoxin, the diphtheria immunity level was wrongly indicated by the Schick test. The passive hemagglutination reaction has proved to be adequate to mass-screening investigations being capable to replace Schick test.