title: Comparison of different methods and times for reading the tuberculin skin test.
abstract: BACKGROUND
  Current guidelines vary on the recommended method and time for measuring tuberculin skin test (TST) indurations.
  
  
  OBJECTIVE
  To evaluate the best time and method for assessing TST results and which purified protein derivative (PPD) to administer.
  
  
  METHODS
  Standard PPD (PPD-S) and PPD-RT23 were applied concurrently on each forearm in random order in 78 nurses.
  
  
  METHODS
  TST induration was measured at 48, 72 and 96 h by two nurses by palpation and a ruler, palpation and a Vernier caliper, ballpoint pen and a ruler or ballpoint pen and a Vernier caliper. TST differences were assessed using mixed-effects analysis. We also assessed the rate of false-positive/-negative results and the variability of the TST measurements.
  
  
  RESULTS
  We performed 767 TST measurements. The adjusted mean TST size was larger with PPD-S than with PPD-RT23 (12.8 vs. 10.8 mm, P < 0.001), and at 72 h than at 48 h and 96 h (13.4 vs. 11.8 vs. 10.1 mm, P < 0.05). The smallest number of false results was observed with PPD-S, the ballpoint pen-ruler and at 72 h; palpation+ruler had the least variability at 72 h.
  
  
  CONCLUSIONS
  The TST should ideally be performed with PPD-S and measured at 72 h with the ballpoint pen+ruler or palpation+ruler methods.
authors.affiliation: Division of Respirology and Critical Care Medicine, Queen's University, Kingston, Ontario, Canada.
authors.forename: O
authors.initials: O
authors.lastname: Morán-Mendoza
authors.forename: M C
authors.initials: MC
authors.lastname: Tello-Zavala
authors.forename: M
authors.initials: M
authors.lastname: Rivera-Camarillo
authors.forename: Y
authors.initials: Y
authors.lastname: Ríos-Meza
mesh_terms: D000328:Adult; D005188:False Negative Reactions; D005189:False Positive Reactions; D006801:Humans; D008875:Middle Aged; D017410:Practice Guidelines as Topic; D013997:Time Factors; D014373:Tuberculin; D014374:Tuberculin Test / Q000295:instrumentation / Q000379:methods*; D014376:Tuberculosis / Q000175:diagnosis*; D055815:Young Adult
chemical_list: D014373:Tuberculin