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Reliability of Tuberculin Skin Test Measurement

Jacques Pouchot, MD; Anne Grasland, MD; Carole Collet, MD; Joel Coste, MD, PhD; John M. Esdaile, MD, MPH; and Philippe Vinceneux, MD
[+] Article and Author Information

From Hopital Louis Mourier, Colombes, France; Hopital Cochin, Paris, France; and Vancouver Hospital, Vancouver, British Columbia, Canada. Acknowledgments: The authors thank Christine Chandemerle for her help in collecting the data. Requests for Reprints: Jacques Pouchot, MD, Service de Medecine Interne V, Hopital Louis Mourier, 178 rue des Renouillers, 92700 Colombes, France. Current Author Addresses: Drs. Pouchot, Grasland, Collet, and Vinceneux: Service de Medecine Interne V, Hopital Louis Mourier, 178 rue des Renouillers, 92700 Colombes, France.


Copyright ©2004 by the American College of Physicians


Ann Intern Med. 1997;126(3):210-214. doi:10.7326/0003-4819-126-3-199702010-00005
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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.

Figures

Grahic Jump Location
Figure 1.
Top.Middle.Bottom.

Intraobserver reliability for the ballpoint-pen technique. Differences between the repeated measurements taken by observer 1 (M1Obs1 and M2Obs1) that were obtained using the ballpoint-pen technique are plotted against the mean of repeated measures. Interobserver reliability for the ballpoint-pen technique. Differences between the first measurement taken by each observer (M1Obs1 and M1Obs2) that were obtained using the ballpoint-pen technique are plotted against the mean of these first measures. Interobserver reliability for the palpation technique. Differences between the measurement taken by each observer (Obs1 and Obs2) that were obtained using the palpation technique are plotted against the mean of these measurements. The horizontal lines in all panels indicate the mean difference (thick line) ± 2 SDs (thin lines). The closed circle with an asterisk in each panel corresponds to the superposition of the measures of 27 persons. Areas of imprecision (bars) that were derived from the SDs of the differences were defined for the 10-mm cutoff point for all comparisons. If a first measurement falls within this area, particularly at or about the cutoff value, a second measurement would probably be sufficiently different to lead to reclassification of a negative result of the tuberculin skin test as positive or vice versa. Conversely, such reclassification would occur in only 5% of the cases whose values lie outside this area. Open circles represent patients for whom the tuberculin skin test result was reclassified after the second measurement (all had a first measure that fell in the area of imprecision). Open circles with a number correspond to the superposition of two or four patients. The □s in the top and middle panels represent patients whose test results were reclassified after the second measurement even though their first measurement was outside the area of imprecision.

Grahic Jump Location

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