title: Tuberculin skin test reaction and body mass index in old age home residents in Hong Kong.
abstract: OBJECTIVE
  To study the relationship between body mass index (BMI) and tuberculin skin test (TST) reaction in predicting the development of active tuberculosis (TB).
  
  
  METHODS
  A follow-up study.
  
  
  METHODS
  Old age homes.
  
  
  METHODS
  Three thousand six hundred five residents who took part in a screening program for TB and had two-step TST using two units of the tuberculin PPD-RT23.
  
  
  METHODS
  Rate of development of active TB in these residents over an average follow-up period of 2.5+/-1.25 years.
  
  
  RESULTS
  After one-step and two-step testing, 46.3% and 69.6% of residents, respectively, had positive TST reactions (> or =10 mm). Thirty-four residents developed active TB (323 per 100,000 person-years) during follow-up. The only significant risk factors associated with development of active TB were positive TST according to one-step testing (adjusted odds ratio (OR)=2.91, 95% confidence interval (CI)=1.26-6.74) and a BMI less than 18.5 (adjusted OR=3.15, 95% CI=1.45-6.86). Residents with a BMI less than 18.5 and a negative TST also had greater risk of active TB than residents with a BMI greater than 18.5 and negative TST (adjusted OR=4.36, 95% CI=1.04-18.3), whereas those with a positive TST had the highest risk (adjusted OR=10.2, 95% CI=2.63-39.4). Two-step testing increased the sensitivity but reduced the specificity of TST in identifying active TB on follow-up.
  
  
  CONCLUSIONS
  In the elderly population, interpretation of TST should take into consideration the BMI of the individual. A positive TST according to one-step but not two-step testing was useful in predicting the development of active TB on follow-up.
authors: Division of Respiratory Medicine, Department of Medicine, University of Hong Kong, Hong Kong, China. mmwchan@hkucc.hku.hk
authors: Moira
authors: M
authors: Chan-Yeung
authors: David L K
authors: DL
authors: Dai
authors: Amy H K
authors: AH
authors: Cheung
authors: Felix H W
authors: FH
authors: Chan
authors: Kai-Man
authors: KM
authors: Kam
authors: Cheuk-Ming
authors: CM
authors: Tam
authors: Chi-Chiu
authors: CC
authors: Leung
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D005260:Female; D005500:Follow-Up Studies; D006707:Homes for the Aged; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D008297:Male; D014374:Tuberculin Test; D014376:Tuberculosis / Q000175:diagnosis* / Q000453:epidemiology / Q000401:mortality