title: Causes and prevalence of inadequate pulmonary function testing among patients with systemic sclerosis.
abstract: BACKGROUND
  Spirometry is a screening tool for evaluating the degree of restrictive lung disease in systemic sclerosis (SSc). Observations indicated that some patients could not complete the test. The aim of the study was to identify the prevalence, causes and clinical predictors of an inadequate pulmonary function test (PFT) in SSc.
  
  
  METHODS
  A cross-sectional study was performed among SSc patients over 18 years old followed up at Srinagarind Hospital, Khon Kaen, Thailand, during January 2006-December 2012. The adequacy of the PFT was based on the acceptable blow criteria as set out by the American Thoracic Society and the European Respiratory Society 2005 Standardizations of Spirometry.
  
  
  RESULTS
  Two hundred and forty-nine patients were included (female to male ratio was 2 : 1). The mean age at performing PFT was 51.4 ±11.1 years (range: 19.6-79.5). Median duration of disease at performing PFT was 2 years (IQR: 0.6-4.4). Inadequate PFT occurred in 73 cases (prevalence 29.3%: 95% CI: 23.6-35.0); the majority (60 cases; 82.2%) had an expiration time < 6 s and the others were due to plateau < 1 s (11 cases; 15%), air leak around mouth piece (1 case; 1.4%) and hesitation (1 case; 1.4%). Thirteen of 73 (17.8%) had an unusable graph with the overall prevalence of 5.2% (95% CI: 2.4-8.0). The factor associated with inadequate PFT was docy mass index (BMI) < 18.5 kg/m(2) (OR = 2.17: 95% CI: 1.49-3.17); the same factor was associated with an unusable graph, which was confirmed by the multivariate analysis (OR = 5.21; 95% CI: 1.60-16.95).
  
  
  CONCLUSIONS
  One-third of Thai SSc patients had an inadequate pulmonary function test - the majority because of inadequate time for expiring. Low BMI influenced the effectiveness of the test, leading to an incomplete graph for evaluating lung disease in SSc.
authors.affiliation: Department of Medicine, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand.
authors.forename: Pichaporn
authors.initials: P
authors.lastname: Sumphao-Ngern
authors.affiliation: Department of Medicine, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand.
authors.forename: Chingching
authors.initials: C
authors.lastname: Foocharoen
authors.affiliation: Department of Medicine, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand.
authors.forename: Watchara
authors.initials: W
authors.lastname: Boonsawat
authors.affiliation: Department of Medicine, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand.
authors.forename: Ajanee
authors.initials: A
authors.lastname: Mahakkanukrauh
authors.affiliation: Department of Medicine, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand.
authors.forename: Siraphop
authors.initials: S
authors.lastname: Suwannaroj
authors.affiliation: Pulmonary Investigation Unit, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand.
authors.forename: Uraiwan
authors.initials: U
authors.lastname: Sae-Oue
authors.affiliation: Department of Medicine, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand.
authors.forename: Sittichai
authors.initials: S
authors.lastname: Netwijitpan
authors.affiliation: Department of Medicine, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand.
authors.forename: Ratanavadee
authors.initials: R
authors.lastname: Nanagara
keywords: forced vital capacity; pulmonary function test; scleroderma; systemic sclerosis