Reliability of tuberculin skin test measurement.

BACKGROUND

Important management decisions depend on results of the tuberculin skin test. However, the test is subject to several potential errors, and its reliability has not been adequately studied.

OBJECTIVE

To ascertain the reliability of tuberculin skin testing.

DESIGN

Cross-sectional study.

SETTING

University hospital.

PARTICIPANTS

96 persons who received a tuberculin skin test.

MEASUREMENTS

Ballpoint-pen and palpation measures of induration.

RESULTS

Global intra- and interobserver reliability coefficients of the ballpoint-pen technique were high. Five percent of the time, however, a second measurement by the same observer could be at least 2.7 mm less to 3.0 mm more than the first measurement and the measurement from the second observer could be at least 3.4 mm less to 3.7 mm more than the measurement from the first observer. This could lead to the reclassification of a positive test result as negative or vice versa. The area of imprecision was 38% less broad for the ballpoint-pen technique than for the palpation technique.

CONCLUSION

Reading of tuberculin skin tests may frequently result in misclassifications when measurements are close to the cutoff point that separates negative from positive results.