The frequency distributions of induration measured by the two methods are shown in the histogram of Figure 1. The induration ranged from 0 to 26 mm for the palpation method and from 0 to 28 mm by the pen method. Of the total of 1,340 tuberculin skin tests, 1,095 by palpation and 1,093 by the pen method were found to have an induration equal to or less than 5 mm (negative reaction), 1,055 subjects had no reaction at all by the two methods and were considered as zero responders; 5 to 9 mm induration (doubtful reaction) was found in 49 by the palpation method and in 46 by the pen method; 10 mm or greater was found in 196 by palpation and 201 by the pen method.
Figure 2 is a plot of the indurations found by the pen method against the measurements of the palpation method of 285 subjects who showed measurable reaction. A highly statistically significant linear relationship (r = 0.94) was found with a regression equation of pen = 0.372 +1.0055 palp. This line has a slope of 1.00 and did not differ from the line of identity (Fig 2). Using palpation as the “standard” method, the results of the pen method were analyzed according to measurement of the induration. Measurements were divided into three categories—negative, <5 mm; doubtful, 5 to 9 mm; and positive, ^10 mm. The positive group was subdivided into four subcategories of 5 mm difference (Table 1).
Figure 1. Histogram of frequency distributions of induration measured by the palpation and pen method.
Figure 2. Plot of measurements of induration of tuberculin reactors by the pen vs palpation method.
Table 1—Fnlpation vs Fen Method, When Falpation was Used as the Standard Method