Skin Test Analysis
As described previously, in order to maximize sensitivity our original protocol specified that any induration noted at an early skin test reading would be defined as a reaction and the patient would receive a chest roentgenogram and a referral to the local public health office. We performed a study to ascertain whether this was an appropriate decision. Ninety-six unselected patients and hospital employees who presented for skin testing and were available for both a 24- and a 48- to 72-h reading were studied.
The presence of 10 mm or more of induration at the 48- to 72-h reading was defined as a positive reaction. When the presence of any induration was defined as a positive reaction at the 24-h reading, the sensitivity and specificity of the 24-h reading was 75 percent and 95 percent, respectively. When 5 mm or more of induration was required for the 24-h reading to be defined as positive, the specificity rose to 97 percent while the sensitivity remained unchanged at 75 percent.
These results suggest that the number of false-positive early readings could be minimized by requiring 5 mm of induration for an early reading to be defined as positive and that this would not result in a major loss of sensitivity. Accordingly, the results that follow will be presented using a cutoff of 5 mm of induration to define a positive early reading.
During the study period, 1,533 women were admitted for delivery who had no documented prenatal tuberculosis screening. Of these, 1,456 (95.0 percent) patients completed the Rapid Tuberculosis Screening Program (Fig 2).
Figure 2. Results of the symptom questionnaires, tuberculin skin tests, and chest roentgenograms for the patients screened with the Rapid Tuberculosis Screening Program.