Comparative Results in the Use of Two Commercial PPD Skin Tests in 569 Admissions

¹ Medical Director, Southeast Florida Tuberculosis Hospital.

This study was undertaken to determine the role of intermediate and second strength PPD in the diagnosis of tuberculosis and in addition, to determine if possible whether there might be any differences in the manufacture of PPD. Two commercial brands of PPD were used, one being given on the volar surface of one forearm and one on the other.

If these tests were negative, the same strength intermediate OT was given and if the patient again failed to react, a second strength PPD was given. The degree of induration was measured at 48 hours and at 72 hours under four headings, namely. 0 mm. to 5 mm., 6 mm. to 10 mm., 11 mm. to 20 mm., and 21 mm. or over.

Seven (1.2 per cent) of the cases reacted only to second strength PPD. So far as diagnosis is concerned, a second strength PPD is reliable as an exclusion test for tuberculosis; however, a negative intermediate PPD does not rule out tuberculosis. Although there were definite differences in the degree of reaction to the two commercial tuberclins, when one was positive the other was always positive. These differences in reaction are therefore not important so far as diagnosis is concerned.