title: Low body mass index is associated with a positive response during a head-up tilt test.
abstract: BACKGROUND
  To describe the association between body mass index (BMI) and a positive response during a head-up tilt test (HUT) in patients referred for an investigation of syncope.
  
  
  METHODS
  Observational study of patients referred for the diagnostic evaluation of syncope. Patients were divided into four groups according to their BMI: <18.5 kg/m(2), 18.5-24.9 kg/m(2), 25-29.9 kg/m(2), and > 30 kg/m(2).
  
  
  RESULTS
  A total of 419 patients were evaluated. The mean age was 43 ± 22 years, and 62% were female. The prevalence of a positive tilt test was different between groups when stratified by BMI (P = 0.01), with a higher proportion of patients with positive tests among those with BMI <18.5 kg/m(2) compared with other groups (P = 0.05). Multivariate analysis also showed that underweight patients had a 3.9 times higher risk for a positive HUT response (P = 0.01); additionally, the use of contraceptive drugs was associated with a protective effect during HUT (odds ratio: 0.35, confidence interval: 0.19-0.45, P = 0.001).
  
  
  CONCLUSIONS
  In our sample, changes in BMI are associated with a positive response for HUT, and oral contraceptives seemed to protect against this response. Further studies are needed with larger numbers of patients to corroborate this finding.
authors.affiliation: Electrophysiology and Tilt Department, Instituto de Cardiologia do Rio Grande do Sul - Fundação Universitária de Cardiologia do Rio Grande do Sul, Porto Alegre, Brazil. tiagoleiria@yahoo.com
authors.forename: Tiago
authors.initials: T
authors.lastname: Luiz Luz Leiria
authors.forename: Sônia Regina
authors.initials: SR
authors.lastname: Barcellos
authors.forename: Maria Antonieta
authors.initials: MA
authors.lastname: Moraes
authors.forename: Gustavo Glotz D E
authors.initials: GG
authors.lastname: Lima
authors.forename: Teresa
authors.initials: T
authors.lastname: Kus
authors.forename: Juarez Nehaus
authors.initials: JN
authors.lastname: Barbisan
mesh_terms: D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D001835:Body Weight; D001938:Brazil / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D015203:Reproducibility of Results; D018570:Risk Assessment; D012307:Risk Factors; D012680:Sensitivity and Specificity; D017678:Sex Distribution; D013223:Statistics as Topic; D013575:Syncope / Q000175:diagnosis / Q000453:epidemiology* / Q000503:physiopathology*; D018667:Tilt-Table Test / Q000706:statistics & numerical data*; D055815:Young Adult