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Clinical Investigations: TUBERCULOSIS |

Tuberculin Test Measurement*: Variability Due to the Time of Reading

Dave Singh, MD; Chris Sutton, PhD; Ashley Woodcock, MD
Author and Funding Information

*From the North West Lung Research Center (Drs. Singh and Woodcock), South Manchester University Hospital Trust, Wythenshawe, Manchester, UK; and the Statistics Group (Dr. Sutton), Faculty of Science, University of Central Lancashire, Preston, UK.

Correspondence to: Dave Singh, MD, Lung Function Unit, North West Lung Research Center, South Manchester University Hospital Trust, Southmoor Rd, Wythenshawe, Manchester M23 9LT, United Kingdom; e-mail: dave_sd@hotmail.com



Chest. 2002;122(4):1299-1301. doi:10.1378/chest.122.4.1299
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Study objectives: It is recommended that the PPD Mantoux tuberculin test be read at 48 or 72 h. We have compared the measurements at these time points.

Design: A 10-tuberculin unit (TU) PPD Mantoux test was administered to 116 healthy subjects (76.7% with bacillus Calmette-Guérin scars).

Participants: One hundred sixteen healthy adult volunteers were recruited (health service employees, 29 volunteers; general public, 87 volunteers).

Results: The measurements made at 72 h were significantly higher than those made at 48 h (median, 9.4 vs 4.95 mm, respectively; p = 0.017). In those subjects with induration at either or both time points (n = 69), the readings taken at 72 h were on average 1.7 mm (95% confidence interval, 0.4 to 3.0 mm) larger than those at 48 h. Using an induration of > 15 mm diameter to define a positive result, there were more positive test results at 72 h (36) compared to 48 h (28), with the results from 10 subjects (8.5%) changing because of the time of measurement.

Conclusions: This study demonstrates that, in adults, the size of the 10-TU Mantoux reaction is significantly larger at 72 h compared to the reaction at 48 h. In clinical practice, tuberculin tests should be read at 72 h as negative tests at 48 h may be false results.

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