The influence of local factors on the reaction to tuberculin. 1. The effect of injection.

Forty-three patients being evaluated for the presence of clinical tuberculosis received careful simultaneous cutaneous tests with intermediate-strength tuberculin, comparing reactions elicited with intradermal tests to those elicited by subcutaneous tests. In another study, reactions elicited by 0.1 ml of tuberculin were compared to those elicited by 0.05 ml of the same material in the other forearm. Analysis of scattergrams comparing sizes of reactions to each technique show that differences in the sizes of the reactions elicited by intradermal and subcutaneous tests are usually small and insignificant, but subcutaneous tests unexpectedly were found to often produce larger, rather than smaller, reactions. Likewise, differences in cutaneous reactions to 0.05 and 0.1 ml of tuberculin were not impressive. We conclude that the common impression that errors of technique in the application of cutaneous tests are common explanations for false-negative tests is unwarranted.