Dual skin testing with Mycobacterium avium sensitin and purified protein derivative to discriminate pulmonary disease due to M. avium complex from pulmonary disease due to Mycobacterium tuberculosis.

Skin testing with Mycobacterium avium sensitin (MAS) RS 10/2 and purified protein derivative (PPD) was conducted on patients with pulmonary disease due to M. avium complex (MAC) or Mycobacterium tuberculosis (MTB) and no known immunodeficiency. Reactions > or = 5 mm to either MAS or PPD were present in 37 (84%) of 44 MAC patients and 28 (97%) of 29 MTB patients. MAC patients had a mean MAS reaction of 13.8 (+/-8.3) mm and a mean PPD reaction of 3.5 (+/-8.6) mm (P < .001). MTB patients had a mean MAS reaction of 17.9 (+/-9.4) mm and a mean PPD reaction of 22.9 (+/-11.4) mm (P < .001). MAS-dominant skin tests (MAS reaction > or = 5 mm larger than PPD reaction) were present in 32 (73%) of 44 MAC patients and 1 (3%) of 29 MTB patients. MAS-dominant skin tests had a specificity of 97% for discriminating MAC disease from MTB disease.