title: Tuberculin test measurement: variability due to the time of reading.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  A 10-tuberculin unit (TU) PPD Mantoux test was administered to 116 healthy subjects (76.7% with bacillus Calmette-Guérin scars).
  
  
  METHODS
  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.
authors.affiliation: Lung Function Unit, North West Lung Research Center, South Manchester University Hospital Trust, Southmoor Road, Wythenshawe, Manchester M23 9LT, UK. dave_sd@hotmail.com
authors.forename: Dave
authors.initials: D
authors.lastname: Singh
authors.forename: Chris
authors.initials: C
authors.lastname: Sutton
authors.forename: Ashley
authors.initials: A
authors.lastname: Woodcock
mesh_terms: D000328:Adult; D001500:BCG Vaccine; D015331:Cohort Studies; D005188:False Negative Reactions; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013997:Time Factors; D014374:Tuberculin Test / Q000379:methods*
chemical_list: D001500:BCG Vaccine